I did wonder how you guys are getting on with the vacuuming this type of yr
We have done a few roofs since xmas vacuuming has been a nightmare with blockages as pieces of moss are frozen solid... no chance!
But yes cant see why you cant convert Billy goat - simple hose reduction, we use several for litter collection largest VQ - that particular mc has 5" hose bore with 4m length wand. However it is a 'large' piece of kit, could possible substitute frame to trolley, But would still have to be a large 'footprint' to compensate the impellar movement. Suction on it would be more than adequate. The pain would be the bag, as it gets wet suction would decrease and you would need to clean it daily at least. (pressure wash or industrial washing mc)
With your 'std' vac is the internal hose bore smooth or helix ? Our vac works superb ... all the blockages are always in the 2" pipe !
Currently snowed off - hence office.