Can methamphetamine speed up the process of getting heroin out of your system?

In short, no. Heroin, opiates, and drugs in general are eliminated most often by the liver and/or kidney's, drug tests usually look for remaining metabolites that your body has converted the heroin (or whatever the drug being tested for) into. Although stimulants may increase overall metabolism to a certain degree, the effect will be negligible. Furthermore, if you are being drug tested for the standard NIDA-5 or extended test, they will test for methamphetamine as well.

Single use of heroin will leave system fairly quickly and I suspect increasing your metabolism will have a greater (although still very negligible) effect on eliminating heroin-metabolites out of your system. If you were a daily or regular user, the drug will remain in your system longer and increasing your metabolism will have even less effect. Using methamphetamine will only complicate the matter. It does not have any direct physiological action on heroin or its metabolites that causes it to be eliminated from the body more quickly. Similarly, you're better of exercising to boost your metabolic rate than taking stimulants; especially dangerous ones like meth at that.