this would go into your extension macro for your agent phones: 

I add uniqueid so i can find the call recording easier after watching the call in the CLI>

[macro-agent-exten]
exten => s,1,NoOp(${UNIQUEID})
exten => s,n,Set(CALLFILENAME=${UNIQUEID}foo)
exten => s,n,Monitor(wav|/dev/shm/${CALLFILENAME}|m)
exten => s,n,Dial(SIP/${ARG1}|${ARG2})