Ok, first off, im not an engineer, nor did I stay in a holiday inn express last night. So, take a few shots of your favorite drink and then maybe you will understand where I am going here...
Basic aerodynamics say that airfoils generate significant spanwise flow as you approach the end of an airfoil, which in turn creates vorticies at the tip of the wing, causing increased drag and decreased lift... a lot of planes have benefited from having winglets fitted to help disipate the spanwise flow, and thus the vorticies and drag, Correct?
So, why not add small winglets to the tips of a prop since they are just twisted airfoils.. if the same theory applies... it should possible to get more thrust out of a lesser horsepower engine due to the decreased drag on the blade tips?
Just some random rambling/thinking.