Copying one particular Pricing Condition Types from Invoice to Credit Memo Req

Hi

We want to know, is there any specific User Exit, which can be used to copy one particular Pricing Condition Types from Invoice to Credit Memo Req document.

Let us say, we have the following pricing condition types in Invoice:

1. Sales Price

2. Discounts

3. Surcharge

4. Freight.

When I create Credit Memo Req with ref to the Invoice, I want to only Surcharge Condition Type value have to be copied into Credit memo req.

Please respond.