nice one!! as they say "that's going to cost"!
you will need at least a rear hanger or you won't have any way of connecting the wheel to the bike! I assume it's a replaceable rear hanger?? if not, then you're pretty bolloxed if it's a carbon frame - if it's alu or steel, then it might be repairable by a good bike mechanic/builder.
assuming you have a replaceable hanger, then if you could replace the standard style with a rear facing one, then you could move towards a singlespeed BUT you'll need to use spacers on your hub to position a rear ring. if you can't get a rear facing hanger fitted, then you can still use a downward facing one (standard type for derailleurs) and replace the mech with a chain tensioner which will take up the slack in the chain. that "might" work with 2 rings at the front if the spacing isn't too wide - alternatively replace the setup with one ring, although you'll need a different BB (one with square taper fittings) and a new suitable crank. I don't think (but I could be wrong) that an external BB setup will take a single chainring.
there's plenty of info and videos on t'web of how to convert a standard setup to a single speed -
Charlie the Bikemonger is a good place to start with his "how to" video - he sells all you need for the conversion. I used him when I converted my old frame into a SS.
Edited: 03/01/2012 at 17:09