The [route] object in Max6 does that. Also you can have a look at [osc-route] on maxobjects.com

"set foo" - [prepend] ?

Or perhaps a custom [js] script within a [p], which creates a certain number of inlets/outlets based upon the messages sent to it? Just a thought.

Here's a little abstraction that uses [route] and [thispatcher] to re-script connections and outlets, it's from my pre-javascript days. I did start a javascript project to do something like this but I shelved it, I think due to javascript's inability to differentiate between float and integer arguments. Anyway, I hope it's useful.

lh.route.maxpat:

lh.route.maxhelp: