The default behavior is to use the calling device's CSS for the redirected calls. In your case it sounds like you want to use the redirecting device's CSS. I haven't tried this myself but I believe you will need to change the following registry entry on your PGs. You will want to use option 2 (ROUTEADDRESS_SEARCH_SPACE).
HKEY_LOCAL_MACHINE\SOFTWARE\Cisco
Systems,Inc.\ICM\IPCCL\PG1B\PG\CurrentVersion\JGWS\jgw1\JGWData\Dynamic
"UseRouteAddressSearchSpace"=dword:00000000
- Used to control behavior on CTI Route Points for Route Selects.
UseRouteAddressSearchSpace can be to set 0, 1, or 2 where :
DEFAULT_SEARCH_SPACE = 0
CALLINGADDRESS_SEARCH_SPACE = 1
ROUTEADDRESS_SEARCH_SPACE = 2