but whether it would still fit in the finished state....
Of course.. no problem at all.. From a screw-cord-screw I first constructed a kind of compass and marked a circle in the appropriate size. Then drill a hole for the jigsaw and saw along the marked circle. Attention: choose a saw blade that cuts "smooth" on the top side. I then sealed the open cut with something (I think it was rubber and silicone).. Put everything in place.. That's it..