Do you want to keep the SSS as single coils, as if so there is not much that can be done. A 10 way freeway switch would probably give you the most options.
Other things you can do is put in single coil size humbuckers such as those made by Seymour Duncan, then you have more possibilities.
Clapton TBX circuit is also something you could consider but you will need to rout the body.
EMG DG20 with the EXG and SPC.
I suppose if you want weird, you could add a switch to put one of the pickups out of phase.