Use a built-in dishwasher as a portable?

Yes, I've done it myself.
You'll need to remove the feet from the frame and add castors. (Little wheels that swivel.)
Build a 3 sided box out of paneling and a piece of countertop for a top.
The setup that connects the hoses to the faucet and the adapter for the faucet itself is available from most Plumbing supply stores or you can get it from the on-line parts department at Sears.
Then get a good heavy duty exrension cord to use as a plug.
You can do the whole project in an afternoon with just basic hand tools