what he needs is to get a head start on the future, a small diesel engine in the nose, turning an electric generator, powering 2 electric engines on the wings, Chevy volt style. and Sonex aircraft have a few electric engines the size of the main wheels in diameter that are the equivalent of 150 Hp.
actually i have been thinking of building a savvy to operate like that, small 2 cylinder diesel turning a small generator, powering an 150 hp electric motor, now with a small diesel, and 110Ltrs useable, and a fuel burn of just over 5 ltrs/hr. and a 150 hp max in the savvy airframe, climb like a scalded cat, loiter for 22 hrs, and land in 50 mtrs!