Add a payment type option to POS for "Sierra Bucks" or Voucher payment type

Students get Sierra Bucks for earning good grades etc. We would like take these "Sierra Bucks" as form of payment on our POS. I see the earned button but this will not work for us as we need to utilize who spent the "Sierra Bucks"/Voucher. Can we add a "User Defined" payment type to allow students to pay with their "Sierra Bucks"/Voucher.