The WRX has the cruise control switch mounted in the steering wheel so when I installed the FFR steering wheel I had to find a place for the cruise switch. I ended up mounting it past the ignition key - still easy to reach.
Subaru gave us a nice strong bracket at the bottom of the steering column to hold the cruise switch. Remove the plastic cover at the bottom of the steering column to find this steel bracket then remove the 3 (very tight!) screws holding the bracket.
I had to cut and bend the edge of this bracket to mount the cruise control switch, in its steel mount, with two bolts. I then cut a chunk out of the plastic cover for the switch. Once connected to the OE wiring the ECU should not know the difference.