So my understanding is A has a IVR received "user id" which is digits and you like to pass them to Tcl,  is that right ? If this is the case and A make a call to Tcl (router) then there is a way.
For example, "A" receive "user id", "7777" then "A" can call to reach Tcl router, say number is 408-555-1234. So instead of calling 4085551234 we can call 4085551234*7777. Then in Tcl use "set dnis [infotag get leg_dnis]" we can get dnis = 4085551234*7777 then we can oarse this string to get user id 7777.
 
Thanks

Yes you can parse string and if you can change ANI in CCX then send to Tcl that even better if you can't then use DNIS = real called number + usedid to reach router (Tcl)
Thanks !
 

for example if you need to call 408321000 to reach router you can use 40832100007777 (7777 is the user id and assuming it's not going thru PSTN)
 
Use set dnis [infotag get leg_dnis]
to get DNIS
or
set sni [infotag get leg_ani]
to get ani
 

If you can not put it in DNIS try put it in ANI.
It's the same if you cannot do it in Tcl I think VXML is the same result.