There are many humbucker-sized P90's out there of all different flavors. That is the closest you will get. There are also humbucker-sized trim rings for single-coil pickups. These would work effectively as well if you wanted to stick with Strat pickups. Alternatively, you could have a company like WD Music or PickGuardian make you a custom pickguard to fit the Jag pickups.
See, you aren't really stuck. It's just going to cost you some money.