At the risk of giving it away, look in a future issue of Professional Pilot magazine for an article on Morphing Rotor Blades (sorry if this sounds like an advertisement...). I know the author well enough that I used to let him sleep with my ex-wife.
Interesting and may be a very good application of the technology for Dave's idea.
The other thought for reducing blade tip vortices is to use very small, powerful, Wheeler-type vortex generators to reduce spanwise flow in the first place. But that's a whole other story…