Use the putty knife is the only advice I have what was your bed Temp when you printed?
Haven't tried it but wonder how Aquanet hairspray sprayed on the blue pad would work? Just don't get it all over the rest of the printer. I have several glass plates making it easy to swap and spray them outside the printer. I also like the glass build plates because when a prints done I just remove the whole plate from the printer and stick it the freezer for 10 minutes. It practically falls off after cooling off.