I considered checking this option before I settled on the rack w/ back rest. It may or may not work...
If you want to retain the seat and not use the Triumph rack that is made to accompany the bar, check your local Harley dealer. They sell a smaller version of the 'solo' seat type (welded wire v. bar) that MAY ( I repeat - MAY) fit in the remaining space between seat and tag bracket. It is considerably smaller, but if it fits the fender contour it may fit your need.
http://www.harley-davidson.com/browse/br...;bmLocale=en_US