How do I legallly install winglets on a standard airworthiness certificate?

A friend in my club built a pair of winglets for his Standard Cirrus.
His glider is expirmental, mine is not. The total cost for him was
just a hundred dollars for supplies, and some free guidance from a
local IA/AP. The finished product looks fantastic! The mold came
from an American Spirit, which I believe is a copy of the Ventus. And
the result is that his handling has improved quite a bit. He did do
some adjustments on the toe-out angle to fine tune it which
supposively helped.

I would like to do the same thing with mine using the exact same
molds. My Cirrus is a standard airworthiness certificate. If I were
to do the factory winglet or the Maughmer winglet, the cost is between
3,000-5,000 when it's all said and done. So that being said, this
option, looks very appealing.

Has anyone in this group dealt with the same sort of deal? I would be
willing to change my standard airworthiness certificate over to an
expiremental if that is the best solution. Any guidance is much
appreciated.

Thanks,
Scott

PS Happy Thanksgiving.