I found that Micador Spray Adhesive (acid free!) works very well for PLA on glass. I have tried this with the bed temp at room temperature and at 70C. They worked very well both times.
Just use a very light coat and it can be reused many times. I haven't tried, but i'm sure it would work just as well of any other plastic used.
The spray adhesive comes off very easy in hot water.
Just thought someone would like to know this. Have fun!