I have an Aspencade and they kinda/sorta self cancel. I cannot see why you cannot wire one in. I'm without my service manuals and schematics and so I am without information.
I do remember his would cancel, the previous owner could have wired one in. It's like the seat on my Aspencade the previous owner took one off an SE and it has a rain cover.
The turn signal cancelling unit is behind the lower left fairing panel. There is a bunch of trouble shooting steps to check out there, and there are also some signal relays in the trunk to check continuity as well. Section 19 pg 25-26 of the service manual. PM me if you don't have one and I can e-mail you the pages.