Need help subbing urine for drug test...

Long story short, I got an internship and they called me a few days ago. I smoked like two days before hand and I know good and well I wont be clean in time, there's just no point in kidding myself. Anyway I have training for this internship on Tuesday and meet with the company Thursday. This is less than a week. They mentioned nothing about a drug test but it's safe to assume there will be one, and I simply don't know when they will want it. I subbed successfully before and it was my first time, but I knew when the test was going to be so I had prep time. But it could be any day for this, and have a source of human urine as well as quick fix synthetic urine as a backup, but what scares me is keeping the temperature in the right range. I'll have about a day of prep time to run tests but I don't know if it'll stay warm when I need it to.
So, what I was thinking was nuking it in the microwave in the morning before training every day, I'll try to have a fresh sample everyday and if not then I'll just use quick fix. But if the test isn't that morning or later that morning, it could possibly cool down below the required temperature, and I need to run tests to see if my body heat will keep it warm but I really doubt it. So I was also going to get hand warmers and see if they can help keep it warm. So what do you think? Any advice?