I'm sorry your only response was from a just-registered self-promoting spammer.

First question- so the existing distance from the wall to the centerline of the closet flange is 11-1/2"? Hope I'm reading that right.

The link below is the Vespin install instructions. It has their Uni Fit setup. I haven't installed one, but I have a general idea how it works. I think Ask This Old House may have shown putting one in a while back (maybe available online).

The good part about the Uni Fit is you trade out a pipe section to adjust the rough in distance. The bad part(s) are that you 1) have to buy/order the different part and 2) have to drill in anchors into the floor for it.

The 12" rough in is designed to put the toilet about 3/4" off the wall (see the section in the manual). With a 11-1/2" rough in, your toilet will only be ~1/4" off the wall. Snug, but I like it that way.

Good luck. Hope that helps.

Here is a link that might be useful: Toto Vespin II install instructions