I encourage you to take a look at
The Blue Alliance's coverage on this topic, and read the show notes. If you can obtain a joystick port extension cable (these contain the full amount of wires, compared to how many a kit joystick would have), and cut it open, you can crimp on quick-connects and use some other small wire to create interconnects to your switches. I will note, this can be a painstakingly long process (I've done something like 50 crimps on our OI this year).
If you look at the joystick pinout in the shownotes however, you'll notice that Port 4 steals some functions from Port 1 so that you can make a more extensive switch box. Port 2 also does this, but if you use 2 sticks for drive, using port 4 makes the most sense. So to wire it up from there you just connect ground + any one of the digital bits to wire a switch into the corresponding variable. If you want to use potentiometers off of the x, y, and etc. lines, I will let a smarter person than me answer because I'm not positive the way I did it was correct.
You'll also need to consider a custom enclosure for it. Radioshack doesn't carry the most suitable project boxes, but specialty electronics stores around you probably would, and you can use a mill, drill, or anything else to cut the holes in the surface of it. Switches that mount circular work best compared to square hinges just due to how hard it is.