1. Create\edit a GPO that applies to all the machines you want to reset the local admin password on.
2. Open it up and go to Computer Configuration -> Windows Settings -> Scripts -> Startup.
3. the command is 'net'
4. the parameters are 'user Administrator whateverpasswordyouwant'
5. The machines local admin password will reset on next boot.
I've just tried this and it worked fine, Thanks for the help.