cgnat ams0 vrf-aware flow data export help

Need assistance with exporting flow data for inside interface of cgnat ams0 aggregated multiservice interface I have MX960 with MS-MPC-128G doing cgnat using AMS0 (aggregated multiservice of underlying mams interfaces) using next-hop-style vrf-aware cgnat. I need the cgnat inside domain interface (ams0.551) to be configured to export flow data (jflow, sflow, ipfix, whichever version i can use) to a flow collector server, this is important so we can have flow data of *pre-nat) private ip traffic. Anyone know how ? -Aaron