Also, If this is possible, would it leave any IO pins free? I was hoping to also be able to connect a solenoid.
It looks like a couple of the pins aren't being used and I wondered if I could still use them.
I've not done it before but in theory it's possible. You'll notice the second header is broken out on top.
That is what I was thinking, although I will need to wire them up with a 10-pin cable or something. I also tried testing the voltage of pin 4 (the MOSI one) with the RFID running. It looks like I can switch the voltage high/low without affecting the RFID module. I then hooked up an LED and nothing exploded...so that is good, I guess.