Find a company that modifies cars for disabled drivers - they may be able to fix a block to the clutch pedal so that you can reach it. (If others use this car, it would need to be easily detached and fitted, obviously)

I had the same problem myself driving a 1947 Humber Hea*** with a fixed bench seat. Things were simpler in those days before seat belts. I managed with a briefcase behind me. Perhaps you could use a garden-chair cushion, the type that ties on to a plastic garden chair and comes with tie tapes stitched in. It's always the clutch that's the problem, isn't it. The other two are within reach of your right leg, but the clutch has to be pushed aaall the way down!

Short-houses of the World, unite!