The bed is of course used to prevent liquid DMT from just leaking into your pipe somewhere etc, but what about this idea: if you use vermiculite or perlite crumbs either in your bong as a bed, or in 'the machine' instead of the whole ironwool thing that should be just about a perfect material because they have incredible microscopic surface area.
The only thing is: you do not want to inhale stuff like that, so all small particulates should be somehow shaken free and sieved out and washed out first (then dry well cause it's 'designed' to retain some water) before you put them in your smoking device. It is inert and doesn't actually vaporize or anything like that - during production it was heated to incredible temperatures and popped like popcorn so it's quite "done" and cooked, but if you're sucking hard on a pipe and there is considerable air flow you don't want any risk whatsoever of microscopic particles being carried along. Diatomaceous earth is therefore absolutely out of the question, it is similar but pulverizes easily so it's pointless to try and get the dust out.
If you like the herbs then by all means, they are a bonus... but others may prefer limiting the intensity or heaviness of the vapor.
In theory / on paper this could be a good idea, but it needs plenty of peer review because nobody likes silicosis.
Edit: shit I tested perlite and it also crumbles... so I'm not sure how easy it is to prevent small particles from getting inhaled, it may depend on the smoking device.
If only there was something similar that doesn't crumble - something that is not porous but only has huge microscopic surface area. Unfortunately the porosity is exactly what gives it a large surface area when broken up! It would just have to be hard enough to not be broken easily by hand... i don't know what material applies.
Possibly heavy processed sorbents such as calcined dolomite or calcined huntite - they are not brittle.
Ironwool it is then :D (burn off the machine oils first before using it!!)