If the call has been put on hold, the other operators would use Pickup and the Operator's extension number, but it's a crapshoot as to which call will be picked up.
You could loop around a few analog stations and loop start lines, put the analog stations in a linear hunt group, assign the lines to the Operators. Direct the incoming calls to the hunt group, now you have a group of buttons shared between Operators that they can answer and transfer.
Once put the actual Operator console in the waiting room, took a non-operator station, gave it 10 SA buttons, and the other "operators" (who were also NOT operator positions) SSA buttons for this main one. Now the incoming calls again looked like a Key system to the Operators, but still PBX operation.