Ah, the drug addict classic. Covering the crash up with opiates--that's what you mean?
There's no dangerous interaction. Just dont push the dose because sometimes the stim come down is quite depressing as you know, and if it doesn't fully cover up the come down you don't want to take more hydro than your tolerance can handle.
Also! If you combine the two the same day the stimulants will cover up the effects of the hydro just a bit--so again you don't want to take more than you know you can handle because of the diminished opioid feeling from the stimulant use. I see nothing wrong with this. As long as you're not doing this quite frequently as opioid tolerance will rise and no longer be effective for the purpose you're posting about.