Just an out of the box thought, what if the last approx 3-500m of the taxiway was wide enough to be like a 2 lane road so that everyone was lined up as now nose to tail in the left hand "holding lane" but could then be called out of that line/lane by ATC so that they can be launched in any order ATC deemed best???
Or something like Rome with 2 holding points each side of the departure runway AA1 and AA2 from memory. 50 seconds between departures for 737 sized aircraft. Granted they seemed to have a dedicated departures runway that doesn't cross the arrival runway. The limiting factor in perth appears to be airspace and separation on the climb though from previous postings here.