That's only 3/4" bigger around than a standard water bottle.

I wouldn't be surprised if a local fabricator could make a bottle cage mount for that, maybe with a buckle straps ala the old fire extinguisher wall brackets.

Considering what you're trying to do you may find someone local willing to put something together on the cheap.

I'm thinking basically a 1" stainless strap w/ a 1/2" bent lip at the bottom and two counter sunk holes for the bottle cage screws and two band clamps welded to it. The hose can be routed up the stem and back, or up the seat post and between your legs, being careful to avoid tangle spots..


And kudos for you for not giving up when the going gets tough.