Excluding Freight&Taxes for Credits/Returns from Billing Document

Hi

We have a requirement to exclude certain conditions (freight and taxes) for credits/returns created with reference to a billing document. Basically we want to refund the value of the goods, but not the associated freight and tax costs associated with processing the order.

We tried creating a pricing requirement against the condition types in the pricing procedure, to exclude these conditions for certain return/credit order types, but this didn't work.

Can anyone advise the correct way to go about it?

Many Thanks

Chris