Slicer software capable of working with large filaments
After checking it up, Ultimaker Cura (and possibly most other slicers capable of multi-extruder setups) is able to handle multiple extruders of varying nozzle size and seems to be ok with 25 mm Nozzles or something ludicrous such as 200 mm filament. You should aid its slicing in some way:


Dedicate one nozzle to the support structure, that's easy.
Design your parts with 2 shells:


One is the main body with corners cut to the main nozzle's extrusion diameter.
The other is the corners and details.