Is this possible (NFC + Mifare cards)

[mrbios]

Using a phone that has NFC, is there any apps that can be given an 8 character hex key of my choosing, and present that to a mifare card reader over NFC?

 

Basically we get some kids whos finger prints don't work with our cashless catering system for some reason, and at the moment we issue them student meal cards, we print off a label, stick it on the card and assign the card to them. However it's both time consuming to do and the kids keep breaking or losing their cards. So I was hoping that in some scenarios the kids could use their mobile phones, swipe that on the till and have it recognise them. As they're far less likely to lose their phones (one would hope) and saves us getting cards made.

 

Any alternative recommendations would be appreciated, I've suggested keyfobs instead but they (being the higher ups) don't like the idea of those for some reason...