Nice to hear that this piece of code is useful.
I was thinking about adding another proximity reader to the same PIC myself too but it was a little bit difficult. As you may have noticed, HID readers are critical: they give a very short pulse (about 40uS) but on the other hand their data "packet" lasts very long (about 70 mS!!).
Long packet is not a problem of course but it takes nearly 36uS for a PIC running @4MHz to branch form "everyday jobs" to card reading.
So if i have 2 readers active at the same PIC chip, it really puts it on the edge.