It is not the kind of attraction that you can put a wheelchair on unfortunately. You have to be able to transfer.
http://www.wdwinfo.com/wdwinfo/guides/epcot/epfw-soarin.htm
"Lastly, on the negative front, guests who use wheelchairs and cannot transfer to a ride vehicle seat will not be able to experience this attraction, as there is no way to accommodate a wheelchair on the ride vehicles. disAbled access to the attraction, however, is good, with wide, gently sloping ramps throughout the queue area, and ample room to maneuver a wheelchair inside the ride theater. You just have to be able to get into the theater seats once you're inside."
Enjoyed the update TK--love the purse--I'm just like you with rides so I'm happy you took the risk for your son. I did Soarin' too and while it still makes me a little nervous I do enjoy it. The things we will do for our kids.
I think I'll try that line on DH next time. "I want something new...something different."