Hi Peter,
I did quick test and here is brief "how to"

1. Put a new block of type "MultiFunction" before your "Selection" block in the strategy ( --- MultiFunction --- Selection)
2. Add following functions/lines to "MultiFunction" block
ExtensionAttach['SIP_REQUEST_PARAMETERS','req-param-1']
ExtensionAttach['req-param-1','local']
3. Save the strategy and test it
4. You should see in SIP Server log that RequestRouteCall has the keys "SIP_REQUEST_PARAMETERS" and "req-param-1" in the Extensions.
[color=navy]message RequestRouteCall
AttributeThisDN '601'
AttributeConnID 007801a94550a002
AttributeOtherDN '301'
AttributeExtensions [265] 00 0C 00 00..
'InfoToSendInInvite' 'INVITE from SIP Server'
[b]'SIP_REQUEST_PARAMETERS' 'req-param-1'[/b]
[b]'req-param-1' 'local'[/b]
'DEFAULT#' '9999'
'CUSTOMER_ID' 'Lab'
'AGENT' '301'
'PLACE' 'Place_301'
'DN' '301'
'ACCESS' '301'
'SWITCH' 'SIP'
'NVQ' 1
'TARGET' 'vg_ServiceA@lab_rut_statsrv.GA'
AttributeRouteType 0 (RouteTypeUnknown)
AttributeReason [14] 00 01 01 00..
'RTR' 116
AttributeReferenceID 19[/color]
5. INVITE issued by SIP Server contains the parameter "req-param-1" in Request URI
[color=navy] INVITE sip:301@172.18.1.1:13312;[b]req-param-1=local[/b] SIP/2.0
From: <sip:303@172.18.1.2:5060>;tag=003BFA42-B380-199A-A590-020112ACAA77-8
To: <sip:601@172.18.1.2:5060>
Call-ID: 003BF9D4-B380-199A-A590-020112ACAA77-4@172.18.1.2
CSeq: 1 INVITE
Content-Length: 0
Via: SIP/2.0/UDP 172.18.1.2:5060;branch=z9hG4bK003BFA56-B380-199A-A590-020112ACAA77-12
Contact: <sip:303@172.18.1.2:5060>
Allow: ACK, BYE, CANCEL, INFO, INVITE, MESSAGE, NOTIFY, OPTIONS, PRACK, REFER
X-Genesys-CallUUID: 01EI265LRCCPL9CG080H5B5AES00000A
Max-Forwards: 69
Session-Expires: 1800;refresher=uac
Min-SE: 90
Supported: timer[/color]
R.