well eg Fuji and Agfa 100 foot bulk lengths came on reels in small cans and if you have three reels you can fill them from a 400 foot can and fill the last 100 foot unto a normal bulk core.

Think you can get the reels on ebay

Takes a while to wind on 100 foot.

A changing bag is ok you can leave the 400 in one side of the can, so no risk of spaghetti, if I can do it you can too.

If Kodak stops 5222, Ilford could do HP5 in 400 and 1000 feet again?

Remjet is not a problem in spiral tanks you can sponge it off afterwards rather than as a pre in the dark job. Don't try in in a mini lab though!