Reduce nesting in expression

I have a large (~2800 characters) function (mathematical function in text format, not code) with a high degree of nesting with parenthesis (more than 32 levels). I need to get it into a more simple form so it's parseable by Matlab (where the upper limit is 32 levels). I know that there are repeating subexpressions within the function that if eliminated (or "simplified" in some way, i.e. identifying and replacing them with a variable such that the subexpression could be evaluated prior to the evaluation of the large function) could allow the nesting level to drop low enough - but I don't know what the subexpression are, only that they exist.

Can anybody suggest a potential solution or Matlab functionality that could potentially lead to a solution?