When we owned our boat company, we had some cardboard plates made up with our Texas Dealer number on them. At the bottom of the plate it said something like

"This boat was recently purchased from _____________ by ___________ on ________ . The owner has XX days to register this craft. It will expire on ____________."

Then it gave the mfg/dealer name and address.

We never had a problem. It also helped them if they had to trailer the boat a long way - and didnt have trailer tags.

I once was pulled over in Bullhead City by AZ sheriff's dept while test driving an unregistered hull that belonged to the local dealer. They asked for my numbers, and I gave them the boat dealer paper work -- it was the manufacturers MSO, made out in the name of the dealership. They left me alone after that. But it helped that the dealership was also the same shop that maintained the sheriff dept outboard fleet. ;)

Check with your dealer -- he might have a temporary tag you can use until your numbers come in.