Hell, load up to rigs, one with coke, one with meth, you take one arm and have a friend help you with the other, or you could just mix the powders (I wouldn't apply heat) and do it like you would the quick-way of doing a speedball...
But since the coke rush is more euphoric then the meth rush, just bang yer coke, rush (sit back for the entire 80 seconds) then load the meth rig and go to town.. or if you want them closer, load both rigs .. actually, go ahead and bang the meth first, then shoot the coke... see what happends... the meth would flood your brain with DA then the coke would suck all that right back up.. could be some combo where each drug is fun but combined you rush for like 2 hours and get an erection.. I dunna, in my meth days, you did other drugs from time to time, but the meth was a constant, every few hours a rig was loaded and we would give ourselves our medicine.. so when we had shooters parties, we were on meth.. the plus for doing meth before a shooters party is that each "mini-crash" isn't is more subtle..