CA Vehicle Code sections 5200-5201 state what the rules are for display of plates in CA.
To put it simply if two plates were issued for your car both plates must be displayed. One at the front of the vehicle and one at the rear. The only members of LE that I know that sweat this are those assigned to traffic divisions. The majority of LE officers probably aren't going to give you a second glance. In fact the next time you are out driving look to see how many front plates you see on high end cars like Porsches, Corvettes, Teslas, Audis, BMWs, Mercedes, and etc. A lot of those cars are put on the dealer's lot without a place to secure a front plate. It is something you're expected to do when the plates come.
I would just drive it until you (when/if) get a ticket. Then, put the plate on in a way that satisfies the requirement, have it signed off, pay the small fee, and submit the paperwork. Then I'd take the plate off again and see how long it takes to get another citation.
There are probably a dozen ways from Sunday to mount the plate without drilling any holes in the bumper.
PRODUCT SUGGESTION for AIRCOOLED BRUCE:
A stainless steel frame that clamps to the bumper bracket and holds the license plate. All license plates are universally the same in regards to the mounting holes. You could come up with a classic version that clamps to the bumper bracket and an outlaw version that clamps behind the body and protrudes from under the body.