What type of devices do they users have? If they need the hold/pickup functionality I would point the main line to a hunt group of three or four phantom numbers set as key system appearances on each phone. Then I label them something like "Main Line 1, Main Line 2, etc." on the phones.
I try to avoid pickup groups except where users have single line analog devices since, like VinceWhirlwind says, it can be done better with VoIP sets.