Helicoils are easy to put in ... you should have plenty of room to do it. Ottawa Fastener Supply in bells corners carries them (permacoil brand, but same thing). You'll need an M12x1.5 insert. The tool to insert it is a rod with a little notch cut into it ... you can buy the kit (expensive), or just use an M12x1.5 bolt ... file a noth in the end to line up with the tab on the insert ... you'll see what I mean when you look at the insert. You just thread it in until it's a bit below the face of the pan (put a touch of red locktite on it), then once it's in, break off the tab with needle nose pliers (watch it doesn't fall in!). Leave it for a bit to let the locktite cure, then put in your drain bolt. Proper torque on that bolt is 23 nm (~17 ft-lbs). Use a 1/4" drive torque wrench.
The ghetto way to fix it would be to just get one of those oversize cutting bolts. It will rethred the pan as it goes in, but that limits you to only a couple of changes before it fails again.
2007 BMW 328Xi Touring, 6 speed