Your idea is good, and the problems are as you have already stated. Realyl it probably would not be that bad to get a machine shop to cut your flats.
You might even be able to rig up a spindle on the lathe itself. Something you could slide using the bed ways as the guide to cut the flats. A little router could be used, although it might take awhile to cut but it still would not be bad. You could bring a mount of the carrage to mount the router. I have seen guys use methods like this to rescrape the ways on a lathe. Ofcourse what they where doing was very envolved and took a lot of work but your little job should be pretty easy.
you could even do something like your jacking method you mentioned and then use epoxy under the clearance area to give it stability after yuo have it set. Or put you flats by hand tools, then bolt mounts to them and use hand scraping and a long straight edge to get you possision right.
I think one way or another with a little thought you could get this and get it right without going to extreeme or high cost. I would go for it and figure it out when I got there.
Jess
GOD Bless, and prayers for all.