^^ Ashes work well. As strange as this may sound, I find the most effective way to smoke DMT out of an ordinary weed pipe is to do the following:
First, select a small piece of bud that is just big enough that it won't get sucked through the hole in the bottom of the bowl. It should be small enough that it doesn't entirely block the passage of air through that same aperture. So it has to be not too bit but not too small, at a size dictated by the diameter of the hole at the bottom of the bowl where you put the materials to be smoked.
Now put that bud in the bottom of the empty bowl in such a way that it would act as an impediment to things getting sucked through the hole into your mouth or into the bong-water. Follow that up with a single layer of bud that is torn into the smallest pieces imaginable. This layer of bud should be enough so as to completely cover the bottom of the bowl, but only in a single layer so there is still plenty of room in the bowl.
On top of that single layer of bud, place ashes from the last time you smoked weed, and sprinkle in a few more pieces of bud town into the tiniest pieces possible. On top of the ashes put another layer of weed torn into the smallest bits you can. At this point the bowl should be two-thirds full, with (from the bottom moving upward) a single nugget to block the hole in the bottom center of the bowl to prevent weed bits and ashes from pulling through, then a layer of bud in the smallest pieces possible, then a layer of bud-ashes from a previous smoke session, then another layer of weed torn into the smallest bits possible.
A grinder works wonders for getting the bud into the aforementioned smallest possible pieces.
On top of this second layer of shredded weed, place the nuggets of golden DMT. Surround them with ashes so as to create a level surface, upon which you will put another layer of shredded bud. Finally, top this all off with ashes, and then with some more shredded weed.
This should result in a bowl-load that completely fills the bowl and bulges slightly upward in the center, so as to be slightly taller than the bowl in the middle of the sandwich. The DMT will be a third of the way down, and there should be at least one layer of ashes and two layers of shredded weed (separated by those ashes) below the DMT. This way when the DMT melts it will melt first onto the weed, and then onto the ashes, forming a sticky sort of conglomerate of weed and ash and molten DMT.
The material on top of the DMT serves to protect the goods. The weed on top of the DMT will be what is directly exposed to the heat of the flame (don't put the flame directly onto it, keep the flame mostly away from this top layer of weed and let the heat light the top layer when you inhale) and after the first hit the material on top should remain lot, so that you only need to bring the flame in close proximity to the sandwich once, with the resulting lit weed performing the heating function for subsequent hits, using the lighter only to relight the top layer if it goes out.
Obviously the more commodious the bowl the better for this purpose. Smoking DMT out of a normal weed bowl isn't ideal, but oftentimes is the only method easily at hand, and will serve its purpose well enough should a vaporizer or an oil pipe not be easily found for those of us that are not in a big city (and even here in Chicago, while tubular glass for crack pipes or regular glass weed bowls are easily found, oil pipes are much less available).
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I see mention of not wanting to smoke your DMT with the complicating factor of an additional marijuana high. All I can say is that in my experience, leaves of mint or whatever else plant matter are too dry and too thin, and burn through essentially entirely from the first hit, and ashes alone both fails to provide enough protection from heat for the DMT and also has insufficient conglomeration ability. That is to say that the ashes are not enough of an impediment to the melted DMT, so that some of it will undoubtably get pulled through the hole in the bottom of the bowl (and ashes alone also will pull through that bottom hole themselves quite readily on the first hit as well, leaving insufficient material to soak up the molten DMT and getting nasty ashes in your mouth or bong-water).
The only effective material for smoking DMT in an ordinary weed pipe is, well, weed, in my experience. Layering weed and ashes and using a small nugget to partially block the hole at the bottom of the bowl are both innovations upon the theme of weed sandwiching DMT that I have invented. Partly blocking the hole at the bottom of the bowl with a moderately small nugget allows you to pull harder and get more smoke without sucking shit into your mouth or into the bong, and layering ashes is designed to allow the conglomeration of the DMT and the weed with a suitable filler material. In this conglomeration the weed serves to soak up the molten DMT, and the ashes both ensures the DMT only goes onto the surface of the weed, not soaking in further, and also absorbs some DMT itself, allowing a moderate flow rate of molten DMT instead of too little flow (all weed) or too much (only ashes).
Hope this helps! Good luck, and have fun!