You're right, I thought of how to do it in 2012 (parameters), then tried to figure how to do parameters in 2008, but in your problem it would be the same parameter.
So, remaining options I can think of (none of them great):
1) Multiple copies of the package with the proc name hardcoded. Least elegant, annoying to troubleshoot, but easy.
2) Have a simple dummy table with an identity column. In the master, truncate and reseed it to start with. Then in the child, insert to it with an output in an executesql task, and use the output in an expression to switch between procedure names (if statement or data flow to a control table).
3) If you create separate SQL agent jobs for running it for each procedure, and then have a "master" job that simply calls those jobs in each step, I believe that by default it will spawn them all without waiting.NOTE: I have not tried this, but have read about it. It would let you avoid the master package altogether if it works.