I think the most critical step towards success of such a thing is getting a few bigger companies in each of the startup areas to offer exclusive intern/entry/mid-level positions to these kinds of people.
I am located in Munich, Germany, not exactly a startup hup, but I have some connections to Berlin and would be willing to annoy my contacts there until they agree.
Also should the plans for my own company work out in the next months, I would be willing to offer exclusive intern/entry/mid-level positions.
Besides this digital Walz it might also be interesting to start a small network for "Global German Tech Talent" or something. I know there are a few germans in the Valley.