response cache for PASS through SOAP Method

Dear Experts,

I have a pass-through-soap proxy and i would like to add response cache in a conditional flow for a soap method.

I have tried many ways to to add response cache policy but "cache key" combination is not working in any ways .

1. Method is POST for the pass-through-soap request .
2. The requirement is only for one soap method for response cache .

Do you have any idea if its possible to use response cache for a pass-through-soap proxy?

Thanks in advance

Sujith Mathew