The metal levers on the earlier ETR series cameras fit perfectly on the ETRSi in place of those accursed plastic levers.
I should add that the metal levers are not directional, so they can be used used in place of both the mirror lockup lever or the multiple exposure lever.
Yep, did it a few years ago with my ETRSi - perfect! One can get a broken ETR series camera for a song (though the working ones are cheap too).