I don't think that is going to work. The only items I can add to an SSRS project are reports, data sources and datasets. I can't even create a folder.
One way for you to proceed is to add a Database project to your solution and put the procs in there.
The absence of evidence is not evidence of absence.
Martin Rees
You can lead a horse to water, but a pencil must be lead.
Stan Laurel