There's no 'clean' way to do it, Pauthowoj. I remember the first 2 weeks after my procedure, it was a bit tricky. I slept on a clean hand towel every night after applying the polyderm to my donor site. Try to sleep on your back as must and best as possible. You don't want the sides of the recipient area to touch your pillow.
So, apply the polyderm to the donor site, sleep on a clean towel (if you can) and don't even think twice about it.
It will get easier and more comfortable in the days to come.