Mounting a TC in reverse in front of the MP-E65 ( don't remember which strength TC) allows it to focus to infinity ! ( or thereabouts). I think there is a thread here on UHH demonstrating this .
since the MP-E hasn't left the house since i purchased it and is bolted and tethered/wired to a vertical bench rig i don't think i'll be trying LordV's idea but the distortion is interesting and i'll try it out on something else.