Fralin makes a great hum canceling P-90 that to my ears sound very much like a P-90. Also, Dimarzio makes several of their standard humbuckers in a P-90 shaped format. TV Jones does as well. Finally, mini-humbuckers as found in a Gibson Les Paul Deluxe might be a good option for you. There are several companies making those, including Duncan, GFS, Lollar, Rio Grande.
In short, you've got a ton of options without resorting to routing the guitar to install regular humbuckers.