Report from a recent holiday (yes, holiday ) in Bulgaria:
NCL-LHR 25 Apr - not really possible to manage Gp0 (1-3 line scanned and straight on to jetbridge) - though I note the report above about them managing pen to jetbridge when held there.
LHR-SOF 25 Apr - success - (T3 big pens) agent at scanner suggested our positioning near jetbridge entry. When this opened he was very pro-active in managing Gp0, and turned back a chancer who was trying to force past us
SOF-LHR 3 May - success - I spoke to the agent who knew about Gp0 and she pointed out which lane would be priority. When the lane marker posts were put out by the staff we were conveniently close to start the queue. Gp0 called, and I didn't hear "0 and 1" before we were scanned and on the jetbridge
LHR-NCL 3 May - success - I spoke to the agent who said we should wait nearby and would be pre-boarded, later overheard there would be 3 Gp0 pax. We were scanned and sat at the top of the escalator. Wheelchair pax arrived later and pre-boarded. Several announcements for groups in order, then held at tensa line before automatic gates. One Gp0 brought through during this, who proceeded down the stairs as we glid serenely down the escalator

It seems that asking discreetly is the best approach. When it works the ability to get baggage stored above/ near row 1 without queue angst is a significant benefit.