Triggering other flow with intent (to send vars)

[vertigo]

I'm trying to have various stages in one flow trigger another flow while telling that flow what stage it's on. This could be done by setting a glovar then executing the other flow and having that flow look at the glovar then remove it (to keep down clutter), and that would be a simple enough solution, but it should be, and appears to be, possible to do this via a broadcast message, i.e. have flow one send out a broadcast with the stage in the extras field, and that would trigger flow 2, which would look at the extras and see what stage flow 1 is on. But I can't figure out how. I've searched, I tried the examples under the broadcast action (of which there's only one, and it's unfortunately no help), I've tried making sense of it by just looking at the various options, but I have no idea. How would I set up the broadcast action and trigger to accomplish this?