[Icky]

I've mixed adderal XR and Dexedrine (separately) with opiates on a few occasions. Adderal XR (25mg) combined with 10 mg oxycodone was very pleasant. It resulted in euphoria and a wonderful sense of well-being and relaxation, but i was still focused and driven to complete my assignments and study for tests. I, however, wasn't dependant on opiates at the time, so the angle you're coming from is a bit different.
I'd say that you'll be alright, as long as you don't over-do it on your dose of smack. Just get your minimal fix, take the adderal, and leave some junk for after you have finished your work/whatever it is that needs to be done. The adderal will make you more lucid while on heroin, but deffinitely try to control your initial dose of H, so as not to render yourself inoperable while the adderal works its magic.

Good luck with it. I know "heroin" and "self-control" aren't exactly synonymous with eachother...