Pretty much all been said. Depending on your dose/day/amount of days you've been taking it, and your body weight/metabolism, it's probably a good idea to wait. It
sounds like you are trying to use heroin to get off the subs. I'm lucky enough to have never taken subs long enough to detox from them (that or I just kept hopping back and forth between heroin and subs so didn't notice). I'd advice avoiding the H all together.
If your goal is to quit, I'd just taper the subs. There's a good chance those "leftovers" might end up as a whole brand-new run and you'll end up back where you started or worse. If tapering off isn't possible, I managed to detox myself from heroin/fentanyl using DXM. Second/third plateau was enough to not notice my detox at all, I tended to go for high 3rd plateau for the fun of it though.

Once I discovered DXM could help me detox, that was actually my first choice after every relapse, even over a detox center. Plus, I didn't have to worry about detoxing from my detox drugs, which was a huge plus in my book. I'm not saying you should do what I did, after all DXM can be addicting for some too. All I know is H is a terrible idea if your end goal is to quit.
EDIT: Wanted to add that if you decide to try the DXM detox, please research it a little first, especially if you have no experience with it. It's especially important to make sure you aren't on anything that would interact poorly with it (like antidepressants). Always be careful with what you put into your body, and don't trust anything anybody (even me) tells you 100%, except maybe a doctor (which I am not).