I recently went thru this. Put on an LSL 7/8" bar. I just went with el cheapo amazon.com bar end mirrors ... they came with the expandable aluminum sleeve thing ... $15 for two mirrors with free shipping! Crazy cheap, and pretty high quality. So my original heavy shinny bar end weights are now in a box in the garage for the rest of their lives.
Sounds like you've already put on bar end mirrors ... and ran the bolt into the original MG bar (that has the insert crimped in there)? Did those bar end mirrors come with any expandable inserts?
There are places that sell just the inserts ... like the "CRG Billet Internal Adapter For CRG Bar End Mirror" ... expandable bolt thing inside the bars, mount the mirror to this. That work?