James, I have not done vent gauges, but do you have room to install a tiny 90* elbow just off the nipple on the back of the gauge? I would butt the two males together (the output nipple on the gauge and one leg of the 90* fitting. If it looks like it will work, slip a tiny length of vac line over that union. Then run the rest of the length of hose off the output of the 90* fitting).
It sounds like it wants to kink from a clearance issue (or is it from the weight of the hose)? I have used metal line - bend it into a smooth radius using a tubing bender. Then slide that over the hose like a sheath. It acts like a guide to make your bend smoothly. Or even use strategic zip ties to suspend and guide the line as it makes its way to where it goes through the firewall, etc.
Good luck bud.