If you're the one selling it, the Bill Of Sale likely won't work unless your name is on the title. And, in Utah, you can't legally "pass on" the title to another owner unless the title is in your name. If you bought it and haven't transferred the title to your name, you can't legally sell it.
You may be able to get some sort of temporary transport registration from the DMV, but if you're not the official owner, you may be hosed.
The dealer plate like you're asking for may be the best (almost) legit method...