I know what I would try.Buy an M10 1.25 pitch helicoil kit,
http://cgi.ebay.com/Helicoil-Thread-Rep ... 563c553e7dand carefully helicoil so the insert if flush with the hole(Where it's broken) but no deeper.There's not a lot of meat left there before you would hit the bottom of that left hand side Engine Head-bolt hence not too deep.If the insert is too long or you think it would go too deep I'd hacksaw it down a bit so you don't have to drill too deep.
Then keeping the broken bit as a Spacer you can re-use an engine bolt but don't take it to recommended torque,just decent hand tight so it can't work lose and even apply a bit of thread lock on the nut.
I rode my Bitsa(Made of bits) CX with an engine bolt thread that had gone for a whole season.Just got round to helicoiling it.A loose engine bolt does add more vibration to the bike but in my case it as not harmed the engine

Also if you know some one good with a Mig welder and the correct wire and gas you can weld alloy.