NFC card circuitry recast in polyester resin rings

How difficult can it be to turn an already ultra-portable NFC payment card into a piece of wearable tech?

As it turns out, Oyster cards that still contain a copper wire aerial - i.e. cards produced before circa 2012 - can easily have their circuitry extracted with the help of a little acetone. The resultant aerial and chip can then be reconfigured to fit into technically anything, as long as the circuitry remains intact.