[font=trebuchet ms]There are some humbuckers on the market that will fit in the same place as a singlecoil pickup. If you have some mechanical skill, and know how to solder, it's a fairly easy task. PonyOne posted a thread in the Tech Talk forum on how to do it. In his case, the body was already routed out for a full-size humbucker, so he only had to buy a different pick-guard.

Another way to go would be to modify the body and pick-guard to accept a full-size humbucker. This takes more skill, and risks ruining the guitar, so it's best left to the experts.[/font]