http://www.tsa.gov/press/happenings/...uirements.shtm
This was posted on June 23, 2008:
"This new procedure will not affect passengers that may have misplaced, lost or otherwise do not have ID but are cooperative with officers. Cooperative passengers without ID may be subjected to additional screening protocols, including enhanced physical screening, enhanced carry-on and/or checked baggage screening, interviews with behavior detection or law enforcement officers and other measures."
If I am interpreting that correctly they will let you fly as long as you submit to invasive searches. A temporary ID is better than no ID.
Email them and get a response in writing. You can take their response to the airport for peace of mind.
TSA-ContactCenter@dhs.gov.
Good luck and let us know how you make out.