Just use a regular RC10 kickup and flatten it until it is just right.
I am in the process of doing the same thing with a B3 kickup so I can reduce caster for carpet/asphalt use. (This will involve making a new top plate from aluminum, but you don't have that problem with a Dual Sport.) Yes, I know I can get different caster blocks to reduce caster, but that ends up giving less than optimal steering geometry.
BTW, I have a Grand Motorsports Dual Sport graphite conversion car for sale if you want another one.
I am in the process of doing the same thing with a B3 kickup so I can reduce caster for carpet/asphalt use. (This will involve making a new top plate from aluminum, but you don't have that problem with a Dual Sport.) Yes, I know I can get different caster blocks to reduce caster, but that ends up giving less than optimal steering geometry.
BTW, I have a Grand Motorsports Dual Sport graphite conversion car for sale if you want another one.