forget modifying it no matter what you try it will move, and make nice crunchy noises. there must be someone around with a bunch of old fixy wheels that could lend you an old shitter.
If you are really keen and know someone with a mig welder, you could probably do it. If you havea spare disc hub you can use that, I did it. I used a front hub and drilled a cog to fit. Put a new axle in, respaced and redished and bingo. Done. Works well too.
Otherwise get an IRO hub. 130mm compatible, cartridge bearings and cheap.
Unless you have track ends (horiz drop-outs) it's gonne be like learning the art of Zen. If you have an old steal frame you can get a local frame builder to weld you some track ends on. some people use ghost rings but other then that just give in now