You don't mention if the tank outlet height is parallel with the tank centre line. But assuming it is, there's the root cause of your problem. Fix it.

The engine being inverted isn't the cause of your problem. An inverted engine will run just as well as an upright one. Starting wise they are more prone to flooding through mishandling, or as in your case an inbuilt flaw. As you've already correctly identified, the cause of your problem is the "considerable" differential between outlet (& presumably median tank) height (?) and your carb height.

Even if you patch the immediate flooding problem, the engine will never run well for the full tank as feed is suction induction assisted by muffler pressure. You'd be pushing uphill even wih crankcase pressure.

The proper solution is to re-engineer by either lowering the tank to lower the median fuel level or raising the engine mounts to raise the carb height. Rotating and mounting the engine upright will also work if it brings the carb inlet approximately level (+/- ½in) with the centre line of the tank.

Using pinch devices to temporarily stop static flooding ain't gonna' work. It's going to start flooding rapidly as soon as you take it off. Even if you're quick, if you're using an electric starter for starting, hydraulic locking and engine damage with this problem is inevitible. If it was me I'd just bite the bullet, get stuck in, and fix the root cause.