Check with your friend, He may have pulled the stock seat and replaced it with the minicell. Try sitting in the boat on the foam alone and see if you like it. You can also add to, or reshape the minicell to suit your backside.
Then maybe add a backband if you need more support.

: I got a used kayak from a friend over the winter and it looks to be in great
: shape except that the seat is no longer attached. I see two holes for
: screws in the seat but nowhere to screw them into the kayak. Under where
: the seat goes is a material that I think is called minicell foam that is
: somewhat in the shape of the seat. It is a White Bros. Kayak made in
: Canada. HELP!!!