I just 'placed' a humbucker in my Jazzy, the original pup cover holds it tightly in place. No need to screw or anything, in fact no one would know you have fitted a humbucker unless they look close up and see there are no pole pieces in the cover holes, just black bobbin.
You may find you'll need a buzzstop though. Because of the extra output that area behind the bridge really comes to life, you get constant secondry harmonics using high gain. The buzzstop breaks the the string length and dampens things down a bit.