On my IB-1Q build I used a Dremel style tool with a square router type bit to remove the excess wood in the control cavity. It was awkward and the bit had to be quite proud of the motorized Dremel so as to access where it needed to go. Several test fits of the socket was needed until a satisfactory surface area for the socket nut was achieved.

The socket is typically fully hidden in the hole when correctly fitted. I had to "clear" the hole on my IB-1Q to allow the socket to sit fully home.