We tried similar idea 5 years ago in GrandPrix-style contest, where traditional handicapping is not possible. I made simple formula for calculating turnpoint barrel radius for individual competitors:

R = D / 2N * ( 1 - k/k0 ) + 0,5 * k/k0

R is radius
D task length
N number of turnpoints
k0 handicap of the best glider participating
k your handicap
All distance units kilometers.

It works well enough if angle between legs is large, out-and-return legs being optimal.