Urethane paints do not need wax for protection. The only reason is to make it a little more glossy.

If the paint is fresh, you can wipe it down with a "glaze". I think Meguiars has one called "Fill 'n Glaze". This will have the same effect as wax, but it does not seal the paint and keep it from drying. It IS water based, so it will wash off.