Mount “ditch spots” on tow hooks? / legality / clamps?

The law, which is pretty uniform across all of North America, says you must have a minimum of 2, and a maximum of 4 LIT lamps on the front of a motor vehicle. That is why on 4 lamp systems with fogs, the fogs won't come if the vehicle's high beams are on, or the high beams turn the fogs off.

I've not seen anything that restricted how many lights you could have, just that you can't light up more than 4 of them at a time.