I didn’t end up writing anything because I found out that multiple others had explained the idea before I was even around. The idea itself is pretty simple: witness data is 75% cheaper than other data, so users sign counterparty txs instead of btc transactions and submit them to a relayer. As part of that tx, they pay a fee in xcp instead of btc, some is burned but most goes to the relayer for their service.
The counterparty txs would be byte encoded and contain the parameters of the tx as well as signature (and possibly some other data like block expiration) from thé wallet issuing the tx. The relayer would take the entire bundle and gzip it and store it in witness data just like and ordinal. (Could even make the bundle an actual ordinal to force exposure to a broader audience)
from @derpherpenstein: