How do I replace the adhesive on the camera cover?

On the back cover of the G1, there's a little plastic cover that protects the camera lens. A few days ago, the cover sheared off. To clarify, here's a word-picture:

Normally, the camera and speaker form a "V" shape (see http://www.flickr.com/photos/tbtechphoto...) where the camera cover is the left line and the speaker is the right line.

In my case, the speaker ended up being the left line and the cover moved so that it formed the right line of the new V-shape.

I've tried to simply press the lens cover back into its place but the cover falls off very easily because the adhesive on the back of the lens cover and the adhesive around the edge of the cover's holder in the back case have picked up dust and clearly, they weren't strongly stuck together from the beginning.

What would be the best way to repair the problem?

10/27/2011 Update:

I bought a replacement back cover from eBay.