Jeez, sorry I missed this tsquared. Was at a fishing tournament in the louisiana swamp all weekend with the TI and 1 ama/aka/haka kit. Worked better than expected in skinny water.
I did get this sorted. I ended up shooting the tranducer through the hull and it still gives me accurate water temps and the same gorgeous DSI images I was getting in the PA.
Your local dealer can get the Hobie thru-hull plugs and a set of rubber plug inserts. Fair price also for how clean they are. I think I paid <$20 for 2 plugs and a rubber kit. Part #'s below:
THRU HULL PLUG - Hobie # 86505611
RUBBER ADAPTER PLUGS - Hobie # 86505701
You can have a look at them here. http://sunjammers.com/kayak-gear/kayak-parts/hobie/mirage-pro-angleer-12/lowrance-ready.html
I can snap a few pics of my install if you'd like.