Hi Kitten,
From what I have seen in triathlons, it sounds like you have the 2 most important elements nailed! As you know, swimming on someones feet or hip is far easier (resistance wise) than swimming out front or off the back!
I think you have 2 options...1) pick the next slowest person in the swim befor you start and make it your goal of the swim just to 'stick' to that person, thats it...stay with them at all costs! and if you get dropped, note where that happened, and the next time make it your goal to stay with them for longer. Once you can do this for the full swim, start looking up the pack for a new 'unofficial training partner'!
2) when and if you do get dropped, have a very specific goal to think about (i.e. a breathing pattern, or a technical aspect like keeping a high elbow on the catch of the stroke) and take the 'performance' aspect out of that training session.
Either of these im sure will help you get to where you want to go!
All the best
Ben