Windows 7: Public use lockdown questions

I am using Windows 7 Professional 64-bit, not in a domain on 120+ public computers (library).

I have used gpedit.msc to lockdown the prototype computer to the way I want it.
However, I am afraid of locking myself out of the computer if I disable the RUN command which is the last piece in securing the machines.

* I think I can lock myself out but then run gpedit.msc from a thumb drive and get in. Unless I also lock out the ability to run programs from a thumb drive (which I have). So...

How can I secure the computer completely using only policies and yet leave myself a way to get back in?

I came from using Microsoft SteadyState for years, but it does not support Windows 7. Windows 7 has a very nice set of policies anyway. I would like to avoid having to buy software to do this.
Thanks!

Lockdown the computer using policies, if you ever need to get in, use Safe Mode.

I found a nice product called Faronics WinSelect. It does not yet work for 64-bit but should this summer.
I need a way to prevent the public from going in so Safe Mode would not work for me.
Thanks!

In the meantime, you could always customise the login screen to show both the Username and Password fields, and then add a "Secret" admin account with a very complicated password. Looks like a very useful application though, thanks for sharing!