I recently started using Micro Kristal Klear to bond clear parts. I just apply it with a tooth pick around the frame of the clear part. Sometimes, depending on how well the part fits, I will just apply it around the corners.
It has a fantastic bond. I've had to really yank off the clear parts before to get them off. And if you do decide to remove the clear part after you've glued it on all you have to do is scrape off the glue, although you might have to touch up the paint where the glue was. But it wont scar the parts at all.
Another great thing is that you can use the Kristal Klear as a filler around the seam between the clear part and the model.
Its similar to Elmer's white glue but it does dry very clear. You can use something like a wet cotton swab to remove any excess glue.