The co-commish should have all the powers of the commissioner, so I don't see why this isn't possible.
There are a bunch of inactive players, none of whom is the commisioner or another co-commish, in my league I want to replace but I can't.
It is a limitation of the current system. They are able to do mostly anything but delete the league or remove players (it's technically built as it not being their league in entirety, so we don't give them that option). It's something we can address in future builds. If you can place suggestions like these in the suggestions forum, that would be great -- we read them all and a lot of what you guys suggest is great -- fleaflicker.com