I'm afraid there's no parameter. The code would have to be customized.
In Tiki 1.10, due out pretty soon, the maketoc tag has been enhanced quite a bit (thanks to nyloth), and may make MAKETOCBOX redundant. See http://zukakakina.com/maketoctest for an example. One thing I haven't gotten it to do so far is actually make a box, despite the argument for that, but am not sure what the hangup is yet. Or if MAKETOCBOX still has a reason to exist, I'll update it to take advantage of the new maketoc features when Tikipedia is revised for 1.10.