Aviation Week has an article about looking at winglets to increase the performance of the V-22 Osprey (paid subscription required):

The ability of the Bell Boeing V-22 Osprey tiltrotor to fly farther, as well as faster, than helicopters has been a key factor in its fight for survival for more than a decade. But now, with both CV-22B and MV-22B versions recently pressed into service on longer-range, self-deployed combat and rescue missions in Libya and Afghanistan, the hunt is on for greater unrefueled performance.

Squeezing more range out of the V-22 is not easy, however. Constrained from birth by the need to fit on the restricted decks of U.S. Navy amphibious assault ships, the tiltrotor was necessarily limited to smaller-than-optimal wing and rotor dimensions leading to an inevitable impact on range. Without the options of increasing wingspan or rotor diameter available to them, designers are taking a leaf out of the Boeing Commercial Airplanes playbook and studying nacelle-mounted “sails” that work on the same principle as winglets.

Although Bell Boeing declines to comment on the development, Naval Air Systems Command (Navair) confirms it is preparing to flight test a modified MV-22 with the upgrade which could boost range by almost 5%. The concept, which was studied by Boeing for the Special Operation Forces CV-22 version as far back as 1994, harnesses the energy from the vertical upwash around the wing and nacelle. In the case of the V-22, Bell Boeing’s research indicates upwash angles of 10-20 deg. around the nacelles at the nominal cruise pitch attitude of 8 deg. The additional upwash velocity produces a propulsive force by tilting the lift vector forward.

I should note that I am not an aerodynamicist, but it looks to me a lot of the gains from these surfaces are from straightening the rotational wash off the props, much in the same way that stators do in a multi-stage turbine.

Because it increases effective wing area, it would have the effect of reducing longitudinal stability, so the flight test regime will target this concern.