Copy the raked back tips and Schumann type shapes used on modern fast gliders. To work best these need to be worked into the shape over the last 20 to 25% of the wing. Just adding a one inch tip block with rake in it won't cut it.

There was also that FAI pylon racer with the very swoopy wing shape. The trailing edge was elliptically swept forward to a straight leading edge and the outer 30% of the wing then adopts the raked back shape. I don't race but there seemed to be lots of pics around of that model with trophies included.