Use Blister pack, that's flat plastic from things that you purchase. ZIP DRY really holds these in place excellently, (by the way, the way you keep ZIP DRY from drying up is store push all the goop out of the nozzle back into the bottle, and use Saran Wrap, under the threaded dispenser (pointy tip) to seal the bottle and not let air get in)). I always use the residue in the cap as I finish up so that I don't waste any, and can reuse the dispenser. I tend to use ZIP DY with a small stick and group some and don't use the dispenser tip.
This blister pack is on everything, the thin Donut Box type plastic windows on the box stuff works really well, as it is very thin. You wash it with soap and water, rinsing thoroughly, and then glue, making sure you have cut the plastic pieces over size so that they will stick. The other method to hold them in place is to use cardboard strips over the excess plastic part, and a cardboard to strip connection, for a mechanical connection. When using ZIP DRY, or UHU glue for plastic to paper, put a lot on, then separate it and the second the strands start to for, that when you press it together, those strands are the matrix strands that hold everything together. Whatever glue you use will be a mechanical connection as the glue cannot penetrate the plastic. So in essence, you're making a glue frame to hold the piece in. You don't need a lot, just enough. Don't use Crazy Glue as the fufmes will cloud the plastic.