Recently I had an idea for a final boss esc character who the PC's find out is pulling the strings behind all of the kickers.  Although it may be a bit out of the ordinary (and proboly against the rules) but I wanted this guy to be like the ultimate demon who (like the devil) has lesser minions in its servitude.  However the only way I could see this working is if the lesser minions (and mid-boss antagonists) were under a "binding" considering the chaotic nature of demons in this campaign and unwillingness to submit to anyone except for a commen goal.  So what I wanted to know was, would it be too over the top to have an NPC antagonist demon be capable of performing sorcery rituals.

I look forward to hearing comments back on this.  Thank you.

Zedekiel, it's a difficult question because some of the assumptions of your question seem to violate the general spirit of Sorcerer already. 

As a rule, demons never perform sorcery.  Never-ever.  This is because sorcery is, thematically (and hence, in Sorcerer, mechanically as well) caught up in issues of Humanity.  Demons, by definition, lack Humanity and therefore have no ability to perform sorcery-by-the-rules.  Demons, however, do have Will, Lore, and Power scores.  So if Satan wants to boss around Beelzebub, that can be modelled by a Will vs. Will role, or Lore vs. Will, or whatever seems to fit in the context of the game.  It's not as "rigid" as a formal binding--but then, this gives a human sorcerer the chance to exploit some cracks in the demonic alliances.

It's worth noting that there are a few ways for a Sorcerer to become a Demon (most notably Lich-ification, but there are others), and any Bindings they might have will survive the transition (barring specific setting material to the contrary).  So, if your boss-Demon is a post-human, he would not be capable of performing Rituals any more, but he could still have a bunch of operative Bindings from before his transition.

The larger issue is that 'final boss' is not really a role supported in Sorcerer.  I recommend you not think of the character that way, because it's just going to provide expectations that may or may not be met.  Consider them as a person, with a particular amount of power and authority, which is turned toward specific goals (his demon Desire), and who apparently likes to work behind the scenes.  That's a much more useful perspective.

In my experience, big bads in Sorcerer are as likely to be allied with or Bound to service by the PCs as they are to be confronted in epic battle.