If my bike wasn't in storage, I'd share a picture of my broken license plate and what I did to fix it.
The break, incidentally was not the Vulcan's fault. It's the fault of having first spent 25 years on my XT.
Why not get a new plate when I registered the Vulcan instead of transfer that beat-up one from my XT, you ask?
Because, like both of my bikes, it's kinda collectible.
I don't know about states where others of you live, but starting some years ago, Maine began stamping motorcycle plates with the words "Ride Safe" along the bottom. There's not really room for that on the tiny plates but there it is anyway. Being preachy, one might add.
Don't get me wrong. I prefer riding safe. Which is to say I prefer riding which means staying safe. But I don't need my license plate to tell me (or others) to Ride Safe.
Rant aside, my old vintage plate says no such thing. It just has a letter and four numbers. As a nifty feature, it also has space around the edges to actually apply the yearly registration sticker!
Best of all, it gets lots of inquisitive looks. Many folks have never seen a plate like that. I actually got pulled over once

for going a tad fast through town on my XT. The cop who pulled me over looked at my license and reg then asked for my inspection certificate.
"My what?" I asked, acting confused.
"Your, uh..." he looks at my license plate and gets confused himself. "Well, I was asking for proof of inspection but I see... uh... well your bike must be an antique or something huh? Oh yeah, the registration says 1980. That's gotta be an antique!"
"Sounds right," I agreed.
"And you don't have to inspect antique vehicles," he continued. "So that must be why you don't have any inspection, huh?"
"I suppose it is," I said, not actually having any idea what the laws were but also knowing I'd never inspected the bike.
He gave me a warning and wished me a good day, reminding me of the ridiculously low speed limit in that area.
Anyway, when I bought the Vulcan and began to transfer the plate, the crack that I'd attempted to fix along the back with JB weld broke again. That forced me into a moment of reckoning in which I would either have to sacrifice my beloved old plate or find a solution like the one you're looking for Jason.
As others have said, the backing plate is key. Combined with a sturdy metal frame (not white metal), the backing plate is what's held my Humpty Dumpty plate together for the last few years. Here's the one I got. It's not cheap, but it's not cheaply made either.
SS license plate frame w/backing plate