Pazza, I know Mars is coming to the rescue on Monday, but I'll try to describe what I did and see if it helps in the meantime...
I could only manage tandem feedng fractious DTs properly when there was someone there to help, so when I was on my own I did this:
Put both babes safely next to me on the lounge (or bed)
Sat on our L shaped lounge (or bed) with my feet up on the longer bit (IYKWIM) of the lounge
Bend one leg up kind of like sitting cross legged with one leg
Put one babe in the upside-down V of my bent leg and bounce that babe
Attach babe 2 and settle down
If babe 1 still crying - gave my finger to him to suck (like your DTs, mine never took to dummies...)
Hmmm....that probably makes no sense and sounds horribly complicated, but it was actually very simple and worked a treat just about every time! Better than having one in the rocker...
Well, hope that helped...