Coding Capacitive Touch with Shift Registers

Hi All!

I think this is the right category. I have an Uno R3, and I'm working on a project that uses capacitive touch. The problem is I need a lot of sensors. I'd rather not use something like a MPR121 because I can only get four to a board, I loose some control, and they're kind of pricey. My preferred choice would be to use shift registers, and I know it's been done, but I'm kind of stuck because I don't know how to switch back and forth between the inputs and outputs. Any suggestions for types of registers, coding methods, etc?

Thanks in advance!