If you're serious, your best bet would be to get a brake so you can offer up the caliper and make a mount to suit. Mock something up in cardboard to start with to get the dimensions and placement right, transfer to a bit of sheet steel (5mm thick would be a rough guestimate to thickness). Adding a diagonal support from opposite the front mount hole to the chainstay wouldn't hurt. Use a hole saw on a pillar drill with the tube held at the right angle to get the mating surface pretty good prior to welding.
The biggest problem will be getting it aligned for welding. If it were me I'd bodge together some kind of bracket which would sit on a simple 'axle' inside the dropouts, with the mount bolted to it (in the correct place) to ensure that the mount remains perpendicular to the axle. It may also be worth tracking down someone with a disc mount facing tool too just to make it all good.
What size wheels are you running? 24" or 26" I'd go for 180mm, 20" you'd get away with a 160mm.
If you can get it sorted easily enough via mates etc then yeah, go for it.