I think easiest way is to pass call through PHANTOM EXTENSION that has a SYSTEM FORWARD/IMMEDIATE path to the desired group. Name phantoms appropriately. Second line of display will say "FWD FROM <name of phantom>". Alternately you can instead use a named CALL ROUTING ANNOUNCEMENT, especially if you want to make an announcement telling caller they've arrived in the group. In this case display second line will say "XFR FROM <name of CRA>".
A very different idea if you're planning to use an ALL-RING hunt group is to put only a phantom in the group. Then put a SECONDARY CALL KEY on the agents phone for each call brand. Call will ring the agents on the named SECONDARY CALL KEY, and agent must press the key to answer...this gives the agent a chance to get his mind in gear for the correct answer script. If you go this route I always create a CRA saying "This call has already been answered" and set a SYSTEM FORWARD/IMMEDIATE path for the phantom so if an agent is not the first to answer he'll get this message instead of ringing the phantom, which might cause yet another agent to answer. Calls from the hung group to the phantom, of course, won't follow this path because HG calls don't follow sys fwd path.