Looking at where the bolt is for the back of your seat, in relation to where the sissy bar sits, I'd bet you that the new seat will fit just fine. When I remove my Mustang seat, I have to remove the top two bolts on the sissy bar and fold it backwards, out of the way. Easy as pie to do so I am not the least bit bothered by it.
If I were you, I'd make one that either attaches to the bottom of the seat pan and comes out between the two seat pieces or one that attaches to the fender rail. Definitely wouldn't pay mustang for it. I can't justify that kind of expense for a bike that only cost me $5k.
Thanks! It's a 2009 Shadow Aero. 750. Other than a few cosmetic changes, it's pretty much the same as your bike. So.....I wonder if that seat on yours would fit mine....