hmmm, my first thoughts are your seat should be slid down and forward but if thats how you like it, I would be looking at making a threaded sleeve bent to the angle you want it at. if you follow.
ie/ Think of a 90deg fuel petcock... same principal but goes onto your solo seat studs.
My springs sit on an angle, then when its all put together I push them forward over the bungs on the frame and its done, all sits nice, looks fine, rides nice. when you lift the seat is the only time you notive the angle.
Pete