Here is a new workflow I'm building:

For now I have a "Set Priority" status where the user manually sets the priority. Eventually I plan to automate this based on Impact level.
In either case, I want the workflow to go down one of the three "In Progress" paths depending on the Priority. P1 would be for Highest, P2/3 would be for High, and P4 would be for the rest.
I've read a ton of articles but have yet to find a way to effect this desired functionality. I'm beginning to think it's impossible in JIRA though it seems like really basic (and desired) functionality.
Can anyone provide some guidance?
Robert