asterisk users - Jul 2005 - call pickup with a variable pickupgroup/callergroup based on context

Hi

If all my calls are hitting one context in sip.conf, from where they are 
passed to extensions.conf, and then passed to appropriate contexts, how 
can I have pickupo features enabled per context, and also define 
pickupgroups, or can i use a variable in sip.conf for this.

I had a lookup at the bristuff setup, and this seems to do it, but I was 
hoping for a simpler :-) setup

Iqbal