DIAMETER: Populate the Subscription-Id-Data AVP 444 from the SIP P-Called-Party-ID

Hi Team
Need some help inter-operating with an open source PCRF.

For the DIAMETER AA Request, the SBC Document States: "The Subscription-Id AVP (AVP Code 443) is used to identify the end user's subscription and is of type Grouped. It includes a Subscription-Id-Data AVP that holds the identifier and is populated from the Request-URI"

However, if the Subscription-Id-Data AVP is populated from RURI (which contains IMSI), the PCRF will reject. PCRF would work if the SIP P-Called-Party-ID or SIP To Header user part is used to populate.

The thing is, I don't know how to store a value on SIP message with sip-manipulation (like store the User Part of P-Called-Party-ID) and use the value on DIAMETER with diameter-manipulation.