I have the same problem in a GP Venus 40 with an inverted Saito 72. There is really no way to lower the fuel tank without compromising the airframe. My solution was to cut a couple of holes in the side of the cowl and run the fuel line out and back in. from there I can crimp the line so fuel doesn't fill up the carb (you have to be careful about a hydro-lock condition on the Saitos. I simply remove the crimp before starting. The siphon actually makes it easier to prime. Once it's running, the mild siphon is not an issue.

Jason