I don't have an answer to your questions about custom sissy bars, but I had a similar problem. I eventually decided that there wasn't a one-fix solution, but rather, I had to take several small steps.
As you know, I bought a H-D 'Tallboy' seat P/N 52000134 first. Then, the sissy bar backrest P/N 52920-98B had to go (that is, the sissy bar is still on the bike, but the padded backrest is removed.) The was important because I also mounted a rider backrest (
http://www.triketalk.com/forum/threa...a-Tallboy-Seat )
Then, since I couldn't go backwards any more, I started expanding foreword.
I started with the DK Custom floorboard 1" extenders P/N DK-TR-FLB-EXT-TG to give me more thigh room. I also had to extend my shifter pegs outward.
Then I bought H-D 1" longer floorboards P/N 50409-04 that put my shoes closer to the floorboards.
Finally, I installed a Softbrake.com rear brake pedal w/ 20° P/N SB-014(P)+1
I also adjusted the handlebars down a few inches.
It wasn't one thing that fixed our problem ~ it was several small steps that eventually resulted in a comfortable ride for two.