The change that allowed Kirk to be selected was the result of the legislature overriding a veto from Romney, so there's not much that a secretary of state could do to impact things. Interestingly enough, had the legislature not done anything, Kirk would now be senator until 2012 based on his appointment from the sitting governor (deval Patrick) at the time the vacancy opened up.
Just read that Mulkulski may retire as well. My, my, my.