External call to Cisco Unity Connection version 9 and SIP Diversion header

[stinkyshoes]

We have a SIP Peer Trunk group between Cisco CM and Freeswitch (B2BUA softswitch). How can we get a call from the Freeswitch trunk to route to a specific Cisco Unity Connection version 9 mailbox? Tried adding a Diversion Header of the original called party(see below). When the call arrives, it looks like a direct call to voicemail and the opening greeting is played. RedirectingId and LastDirectingID are blank (see below). Is there any way to create a Direct Calls Call Routing Table entry to get it to the original called-party mailbox? Or any other way?
Note- the call originates from a CUCM deskphone to a Freeswitch (B2BUA) users' phone and is diverted back to CUCM. The FreesSwitch extension is not a user in CUCM, but has a mailbox on CUC Voicemail.

From Freeswitch to Cisco CUCM: (I wish I had a SIP trace on the CUCM side)
INVITE sip:50000@172.88.88.4;transport=tcp SIP/2.0 (SIP Trunk to CUCM)
Via: SIP/2.0/TCP 172.88.89.4;branch=z9hG4bKH2jejj6m8HB3Q
Max-Forwards: 67
From: "Robert Banks x88678" sip:8168403678@URL.net;tag=QKK19FHHK6eFp
To: sip:59000@172.88.89.4 (Unity Connection access number)
Call-ID: d77f9c40-862e-1233-0f82-40a8f03a26e8
CSeq: 76420517 INVITE
Contact: sip:void@172.88.89.4:5060;transport=tcp;gw=hpbx
User-Agent: FreeSWITCH
Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, UPDATE, INFO, REGISTER, REFER, NOTIFY
Supported: timer, precondition, path, replaces
Allow-Events: talk, hold, refer
Content-Type: application/sdp
Content-Disposition: session
Content-Length: 223
Diversion: sip:58114@172.88.87.41;reason=unavailable
Remote-Party-ID: "Robert Banks x88678" sip:8168403678@URL.net;party=calling;screen=yes;privacy=off

v=0
o=FreeSWITCH 1433495151 1433495152 IN IP4 172.88.89.4
s=FreeSWITCH
c=IN IP4 172.88.89.4
t=0 0
m=audio 18120 RTP/AVP 0 101
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=silenceSuppff - - - -
a=ptime:20


Unity Connection Port Status Monitor:
10:29:05, New Call, CalledId=50000, (Unity Connection access number)
RedirectingId=,
Origin=16,
Reason=1,
CallGuid=21FC2C1261B84E1D988A255814FA7F9E,
CallerName=Robert Banks x88678,
LastRedirectingId=,
LastRedirectingReason=1024,
PortDisplayName=PhoneSystem-1-001,[Origin=Unknown],[Reason=Direct]
10:29:06, AttemptSignIn
10:29:06, State - AttemptSignIn.cde!Dummy
10:29:06, Event is [NULL]
10:29:06, PHTransfer
10:29:06, State - PHTransfer.cde!LoadInfo
10:29:06, Event is [TrueEvent]
10:29:06, PHGreeting
10:29:06, State - PHGreeting.cde!PlayGreeting
10:29:06, Call answered if needed
10:29:07, Playing greeting for Call Handler: Opening Greeting