Mobile User - Temporary Admin Rights

We have a user who regularly travels and sometimes requires the ability to
install software when away from the office.

He, as is everyone else except the I.T dept, is a normal domain user with no
administrator rights.

Is there anyway he can have administrator rights while he is away and not
directly logged onto the domain? We only want these administrator rights
allowed while he is away and not when he returns and actually connects to and
logs onto our domain.

Bear in mind he will still be logging onto the domain (Without actually
connecting to it) when away as he has offline files enabled. EG Log on to:
"DOMAIN NAME" and not "LOCAL COMPUTER".

Thank you.