Have a Machine shop or a frame builder fabricate a overlaying hanger.

A Milling machine , like Bridgeport could, like a router in wood,
thin down the dropout to fit an existing replaceable hanger ,
Machine shop time is not cheap, unless your father or a family member has one..

Dremel hand tools is not going to give you a flat, machined to be that way, surface
that needs to be made for strength and shifting accuracy.

If you aren't budgeting even a hundred for even a IG hub I don't know ..
cheap kludge then eBay it , transfer the problem ..

Though if you convert it to a single speed with an Eno hub, you may be able to sell it , without too huge a loss..

Fixies are a hot market , maybe a Trustafarian with money to burn out there,
you never know..