With this freehub body from Alexrims it is possible to convert your existing hub/wheel to HG 11-speed.

Specifications:

Material: steel 
Cassette compatibility: HG spline L (Road 12/11-speed)
Compatibility hubs: Alexrims/Bear Pawls system
Wheel compatibility: Alexrims CF45, RXD3, CXD4, Boondock3/5, etc. 
Freewheel type: 3 Pawl freewheel 36t
Spring type: coil spring
Bearing: 2 stainless sealed bearings
Color: black
Weight: 151g