It can be be done:
1. Tear down the Nexus 7 until you have the digitizer/ LCD combo
2. Fix the combo by the glas on a heating plate / or a copper or aluminium plate you can heat with a hair dryer. Alternatively fix ist somewhere and put it in the full sun to heat up.
3. Heat it until the combo has 50-70° Celsius
4. Take a ultra strong fishing line or something similar (people proposed E-Guitar strings), attach it to two handles and start sawing carefully through the glue to separate the LCD from the digitizer
5. Remove the glue carefully with LCD Glue remover (lcdglue.com) or Orange Glo
Before trying that, read all the information and watch all the videos in he following posts, so you know what it is all about.
http://forum.xda-developers.com/showthread.php?t=2337288
http://forum.xda-developers.com/showthread.php?t=2317176