Fee Transaction Interceptor

Hi,

I missed the conference this year unfortunately so not sure 100% what level REST services are going to be in.  But if they are at the transaction level, will I be able to design something that will allow us to have a "per ticket" transaction fee, that has a cap.  So for example we have a per ticket fee of 50p, but a maximum fee amount of £2.50.  If a person buys 2 tickets, then the fee is £2.00, however if they buy 10 tickets the fee is just £2.50.

It would be pretty simple to develop the interceptor I think, but its whether you can apply an interceptor to that part of a transaction.