Found this on Reddit. Try it out and let us know. I still don't have my car to test with
"I displayed my Model S in a local green energy fair. I figured out that if you hold the "T" for 5 seconds, you're prompted to enter a code. If you enter "showroom", it enters the vehicle into "showroom mode" and disables driving. However, it does not hide any personal information, so for my local fair, I put my Model S into "valet" mode, turned off "walk-away door lock", and kept the key fob outside the vehicle. This way, personal information was hidden, but people can still play around with the touchscreen."