Series options will get you closer to humbucker-type sounds without changing pickups...
My Xavier hybrid thing replaced my strat, and refined the wiring I had going in there. I routed for a middle pickup and put the L'il Killer from the strat in there, with a L'il Puncher in the bridge and the stock mini-HB (another GFS pickup) in the neck. Each pickup has a rotary switch for local off-split-parallel-series, then there's two toggle switches that allow me to get every possible combination of inter-pickup series/parallel, a third toggle to throw the neck out of phase, and the Tele-switch that came with it acts as a kill/tone-kill switch. It's not technically every possible combination of 6 coils, but there are very few redundancies and only one "gotcha". It is exactly what I would do with a strat (if I didn't already have this...), but I can't really recommend it to random people because it's not super easy to switch from one pickup/combo to another on the fly, and while it feels pretty intuitive to me, it kinda should come with an owner's manual.
Did I mention I have eight of those railbuckers installed? Actually I think it's only seven, but I'm pretty happy with them. Do they sound exactly like a full-sized HB? Probably not, but for the things I would really want an HB sound for, I actually prefer them to the GFS PAF-style in my Xavier SG. The L'il Killer in my hybrid's bridge is heavier wound, louder and darker (in that overwound HB way) than any other pickup I've ever encountered. I don't often play metal, but I do go for those types of tones sometimes, and I have no problem getting them.
Realize, though, that overwound HBs actually work against you when you're shooting for certain types of metal tones. All that extra wire means a lot less top end extension, what some folks might call "bite". If you're looking to sound like somebody playing active EMG-style pickups, you're actually better off with the lightest wound pickup you can find (a light HB in local parallel might be good) and then using a booster downstream to make up for lost output.