Some Rotax two-stroke engines running pre-mix have been used in ultralight aircraft, so I think appropriately sized altitude-compensating carburetors designed to run a petrol-lubricant mixture may be commercially available. However, I imagine it's pretty expensive to put aircraft parts (even ultralight parts) on a racing motorcycle.

These carbs use an aneroid to move a needle valve at the base of the jet as the atmospheric pressure changes, effectively dynamically re-jetting the carb on the fly.