If you want to wire up the switch yourself, it's pretty easy to do if you're a little handy with a soldering iron.
First, make sure that your humbucker has 4 wires coming from the pickup. One (hot) will go to the blend pot, one will be grounded to a pot (probably along with a shield), and the other two leads will be tied together - this is what makes it a "series" configuration - the output of the first coil is tied to the input of the second coil.
On my 4 string, my pickup was wired as follows:
Front Coil: Green (start) -> Black (end)
Rear Coil: Red (start) ->White (end)
If you have a voltmeter, you can verify that you have correctly identified the individual coils by testing the resistance from the assumed start to the assumed end. If you have infinite resistance, then you haven't selected a matching pair of coil leads. Both of your coils should be fairly close to the same resistance.
To verify front/back coil position an analog volt meter works best, but a digital meter may be OK if it's fast enough. Set the meter for the lowest DC volts you can and hook the red lead to the coil start and the black lead to the coil end. Take a large screwdriver or other magnetic metal object and quickly put it across a coil (over the poles/perpendicular to where strings would be) and remove. Repeat with the other coil. The meter should swing one way on the approach and the other way when you remove the item. Whichever coil position causes the largest voltage reading is the coil you have the meter connected to.
Take care to keep track of the start and end for each of your coils. Write it down and/or take pictures.
Once you have identified your coils and wiring, figure out what configurations you would like to have available. There are plenty of choices, but doing more than 3 gets pretty complicated and requires hard to find switches.
I chose to do series, rear coil, and parallel - this required an on,on,on switch. You can find the three position switches at GC or StewMac or other various places online. If you want two positions, you can probably find a suitable DPDT switch at a local electronics store. If you're feeling experimental, you can use some alligator leads to try different configurations before you solder everything to the switch and drill the hole in your pickguard!
Here is a very handy chart that shows the most common configurations:
From a useful TB topic:
http://www.talkbass.com/forum/f38/stingray-mod-adding-coil-selector-series-switch-717929/
Once you've got the leads connected to the switch, connect the output of the switch back to the blend pot where the pick "hot" lead was originally connected, and connect the ground of the switch back to the pot housing that was being used for ground originally. You may need to extend the shielding conductor from the pickup and reconnect it to the ground as well (I did).
Here is a video that shows in-depth how to figure out the humbucker wiring ID:
http://youtu.be/7UfxQBhqen8
