The seat collar isn't a problem, but the lack of cable split-stops is. Were they hacked off by a fixie kid? If so, you'll need to find someone who can epoxy some new ones back on somehow. Or, you could just run cable housing all the way to the rear derailleur and rear brake, and zap-strap them to the tubes. A clamp-on split-stop somewhere at the bottom of the seattube might make a front derailleur usable.