There is a problem if you wire it as a humbucker and drop it into the 550 using standard wiring.
In positions 2 and 4 you'll have some 60 cycle hum instead of them combining properly with the split coil on the full sized humbucker.
If you can live with that simply make sure you're in phase and wire it as suggested, if you would rather have it work as a standard single (keeping hum-canceling in all but position 3, like standard HSH) then you'll have to experiment a bit.
I'm not sure how to wire it with the Ibanez humbuckers to keep things properly phased, but with a set of
Dimarzio humbuckers you would connect the red to ground, black to the input on the switch and tape off the other two, DO NOT connect the other two to anything, DO NOT connect them to each other, just let them hang loose, tape them so they don't short anything.
This will give you the top coil only of the stacked pickup wired as a standard single coil. I've found that while you lose hum-canceling, you end up with a slightly hotter pickup than using both coils.
If if sounds out of phase in positions 2 and 4 simply reverse the white and red wires.
http://www.jemsite.com/tech/img/t_wd_7ap1.gif
This is standard HSH wiring, when you use the HS-2 in single
coil mode it's identical. To have hum-canceling in all 5 positions you'll need something like the Dimarzio 4 pole switch, or the StewMac Super Switch.
I tried it with the Super Switch and it worked fine, but I wasn't all too happy with the sound of the HS-2 with both coils running, so I took it out and wired it like a Jem (I have Evolutions in my 550) and I'm very happy with the results.
Mic