I'm doing some work for TfL at the moment writing the backend for their new website.
Hey did you get anywhere finding out if we can use other NFC devices as Oyster cards in London?
keep in mind that depending on the construction of your sd slot it's possible that the nfc antenna in the card may be blocked by some metal housing.
I wonder if you could get one that fits in the MicroSD slot then has an external antenna - i.e. a metal wire - that you can then glue to the inside of the batter case?