Balk Rule

The 3B doesn't need to hold the runner for the pitcher to throw over. 

True in FED and NCAA, but I don't think so under the (recently changed) OBR.  Under the new rule, a pitcher can no longer fake a throw to 3rd base without first disengaging.  If the throw is to the base, it is not a balk no matter where the fielder is, but if the throw is away from the base, the fielder must be close enough to the runner to make a legitimate tag attempt or it is a balk.

Warning:  Unprovoked smart-@ss comment to follow based on unnecessarily literal reading of the question:

If you throw over and the third baseman isn't covering, you'll have a baseball bouncing around toward the left field corner, and it won't matter if it's a balk or not.  

[Sorry.  I couldn't help myself.]