Nikor made long-roll reels and tanks that would handle the 33ft (250 exposure) or 100ft (750 exposure) rolls from these bulk backs. They were made for field processing of 50 and 100ft movie film but 35mm is 35mm.
I've shot a lot with the 250 back for the original F-1 and the FN-100 back for the newer F-1 and when doing slides it was just a matter of finding someone who did roller transport processing instead of dip n dunk. The last place I used was E-Six labs in Atlanta but they're gone now :-(. I have a big Jobo reel and tank that easily handles the FN-100 rolls...so far I've just been hand inversion processing with it by removing the cog and using an orange cap, but I have a big ATL machine that I plan to use for slides once I get it set up.
Swapping rolls when you hit the end does take a bit longer than with normal 35mm canisters but on the upside there's no rewinding! And a huge benefit overall is there is no felt light trap - the film is just moving through air once the canister is opened up when inside the back.