Check out a Dimarzio Virtual P90. They have two rows of screws (much closer together than what you see on a humbucker) on the top of the pickup so they don't really look like a trad. P90. You may find that you have to do some additional routing to get the cavity deep enough to for a stacked P90.
I absolutely love my DiMarzio virtual P90's but I always have a bit of grit attached to them. I don't play them clean. They replaced some Duncan's that were horribly noisy. I mean bad noisy with any kind of distortion. I have mine switched 5 ways.