Increase Spork Slaves

I can't seem to figure out how to increase the number of spork slaves in Rubymine. I came accross this SO post: http://stackoverflow.com/questions/8396924/how-do-i-configure-spork-to-create-more-than-2-processes and applied the fix to the gem itself, but that doesn't seem to work.

I see that spork can take some command line parameters (like the run/debug). Has anyone managed to increase slaves via Rubymine?

I'm using Rubymine 4.0.2.