Do you have the one-piece seat or the two piece?  I'm familiar with the modding the one piece.  Big Nix has done the two piece and his looks sharp.  On the two piece, since I had moved the rectifier, I shaved off the bump that is over the rectifier until it was even with the seat.  There were also two ridges on the upper back slope of the rider's seat that I also shaved off even.  


You can either shave it off as well or scallop the inside of the foam to fit over the bumps however it won't look as flat.  After I shaved the bumps I cut a piece of aluminum flashing the shape of the entire top of the seat and riveted it on.  I then sprayed the aluminum and seat pan sides with spray adhesive, applied the foam, worked it over the sides and trimmed it with about 3/4" of foam hanging lower than the edge of the seat pan.  At this point the foam held the shape of the seat.  I covered that with two layers of cotton batting also hanging over the edge 3/4".  Added a plastic cover then the seat cover.  Leaving the extra 3/4" of foam and cotton batting below the seat pan edges is important for getting that nice look where the cover wraps under the seat edge.  Trim the extra hangover a tad in areas that may be difficult to staple.  The plastic is for waterproofing and allowing the seat cover to slide and move around when you sit on it.  Throw the cover in the dryer like Big Nix did to allow it to stretch before stapling.  When you put the cover on, snug up the lowest part across the rider's seat first.  Then work outward.  Do a few staples to hold it on, snug it up, a few more staples and so on.