Rename "login hint" sent as optional parameter with oauth authorization request

SSPR has a feature that allows us to use the macro syntax and send extra info as part of an auth redirect to remote OAUTH2 server.

However, it does NOT allow us to rename the prefix... it is always "&login_hint=<whatever macro expanded as>"

I would like to have this string say something else. Anyone know how to achieve this in a vaguely supported manner?