This is a bit of the code I was discussing earlier for refunds through Cybersource. It only works with SOAP for now so keep that in mind. You're free to modify the code, but if you do something interesting, please post it back here in the comments! :)

Download the Cybersource Refund SOAP module Here

Here's the writeup from the module file:

// A quick and dirty module for processing 
//    Cybersource SOAP refunds.
//
// Author: Greg Eisenman
// Date: 5/23/09
//