I know that coke stays in your blood for only like 3 days, Im sure speed is the same way, THC bonds to fat in our blood which is what would fuck you over. MrDank advised me about this sythetic urine stuff that comes with a tab that u drop in and it makes the solution heat up to 95 exactly. I don't know how long you can keep your buddies piss that warm , but even if you do... Dont spill !! lol, good luck bro