TLC script for H323 gateway

Is there any way to forward an incoming call to an external number without tying up 2 lines for the duration of the call? The lines are all analog and PRI Centrex lines. Their current PBX system does this using a flash button the operator's console.  I’ve looked up FXO hook-flash command but I’m not sure if this is what I’m looking for. Basically all calls come into a receptionist and from there they are transferred to the appropriate extensions. Sometimes transferred to other schools across the Centrex lines. How can we accomplish this on their CUCM 8.6 system without tying up 2 lines while the call is in progress?  We are implementing the Cisco Attendant Console and need to have a hookflash key to accomplish this or a key on the Cisco 7960G phone.

I was told it can be done but I need a TLC script to be run on my H.323 gateway.

See if I can understand your question correctly.

Call scenario is that A calls B via H323 GW and actually call will be forwarded to C so A can connect to C without involving  H323 GW

If this is the case it can be by using TBCT

Cisco IOS Tcl IVR and VoiceXML Application Guide - 12.3(14)T and later - Configuring Telephony Call-Redirect Features  […

I also saw some service providers can provide this feature in SIP trunk as well. (using SIP REFER)

Tcl is needed (in both cases) to provide a command to request for this type of transfer. The service provider (external PSTN switch) has to provide the feature to take care of this type of transfer.