[Asterisk-Users] Getting Agent Channel information

[Asterisk]

Given that all agents are on SIP phones (Cisco 7940), and all outside lines
are EuroISDN channels (using a TE405P), is there any way of finding what zap
channel is being used by an agent channel within a dialplan ?

If you type "show agents" on the CLI you get information like:

6038 (Agent 6038) logged in on SIP/6908-8445 talking to Zap/63-1
(musiconhold is 'default')

What I want to get is the "Zap/63-1" information in some form of variable -
I want to do this so that I can use ZapBarge on the Zap/63 channel.

I want to be able to let a supervisor enter an agent number, for the
dialplan to obtain the zap channel of that agent, and then to zap barge it.

I know that I can modify the C code to set a channel variable with this
info, but would prefer to do this within a dialplan, not by modifying the
source.

Thanks.

Julian