Hi Frank,
See attached patch for the ;-trick, that lets you change send destinations on the fly. Variable list length isn't really possible. You can trick around with "prepend" or "glue" but you will also need a variable receiver. I've no idea how to build that.
You could have a look at the flext tutorial example "bind1" (in pd cvs). Also featured in chapter 7 of the flext introduction downloadable at http://www.parasitaere-kapazitaeten.net/ext/flext
best greetings, Thomas