Michael here from Stakewithus.
My team can confirm that this workaround works - we tested it on Osmosis mainnet to allow 1 user to authorize MsgVote for another user via authz module.
TXID: Interchain Explorer by Cosmostation
Evidence of vote:
https://lcd.osmosis.zone/cosmos/gov/v1beta1/proposals/507/votes/osmo1cyyzpxplxdzkeea7kwsydadg87357qnahakaks
I think this will be a good workaround as endorsed delegates’ votes will have priority over validator’s.