And there it left me.  What could Akane do to cure Ranko?  Obviously the 
insult method from the original won't work.

Actually get the shampoo that was supposed to work as a cure.  It existed in
the regular version, but Ranma never got it.  No reason why Akane can't get
it now.

Alternately, you can have Shampoo learn of Ranko's transformation.  Unlike
Kunou, Shampoo believed it when shown it in the original.  There are several
possible reasons for Shampoo learning (ranging from Akane showing, to an
accident, to Cologne showing up and mentioning Jyusenkyou), and several
different reasons why Shampoo might provide the cure once she finds out
(She might even cure Ranko and _then_ try to kill her, out of some sense of
honor.)