Actually, it's possible to use the five remaining clone slots in Project M. In my own personal build, I've added characters WITHOUT BrawlEX, but only certain characters work as of right now. I also can't confirm whether the process is completely glitch-free, although I personally haven't encountered anything too weird. However, for now, I won't divulge the specifics, since I don't want to be responsible for save corruption, bugs, etc. caused by people performing the process incorrectly. Here's a screenshot from PM 3.02, featuring Waluigi and Knuckles. I'd be happy to set up a build of PM with your Ridley once it's finished; it looks phenomenal!