On Valkyrie, I first raised the helm seat by using 1.5 inch thick oak boards, simply removing the seat and drilling holes in the wood in the appropriate places and then replacing the seats with longer screws.
Pics in our album on the above mod.
Also, I had the bottom of the helm seat repadded with denser foam so we don't sink down into the seat as much.
Hope that this helps,
Nick
"Valkyrie"