As has been said in a number of earlier posts on this thread, there is a tendancy to ensure both engines are running earlier than strictly necessary to avoid being embarassed by not being ready on time, and 30 minute taxi times would more than justify using the procedure.
Maybe working a little give and take into your approach to liaising with the jets would be helpful - at the end of the day, nobody screws up on purpose, and we (ought to) understand that everybody is working hard within their own corner of the operation. A friendly "for planning, can you accept [intersection]" would go a long way to ensuring crews can quickly give you what you're asking for - I doubt anybody is going to get worked up if they end up getting full length, and as you say, the gamble of a few extra minutes at idle against knocking 10 minutes off the delay would be taken by everyone I know.
It isn't just the engines that constrain these requests either: If the performance figures need to be recalculated, it will take time to plug the data into the laptop, copy into the FMGC and cross check, and there might be issues in the cabin - after 30 minutes of taxi, and probably another 30 minutes of queueing and boarding, calls of nature may result in the cabin not being secure for takeoff.....we don't just ferry nice docile and compliant people round the skies you know.
Jus in case you take this as a snipe at our friends in the tower, the service we get where I live is fantastic and I've been helped out a number of times with a bit of intersection 'queue jumping' when I've let them know we've been tight on duty limits, so it does work both ways
