In the past I wrote a simple formula evaluator in Python I used to replicate some multicell calculation - the spreadsheet I had took the form of mostly simple algebra being performed in a scanning pattern against various small windows in time (rows) from a set of columns. I just extracted the cell formula definitions and transformed them.

It may not be that hard to replicate the set of formulas you need to get 90%+ of your excel model.

If someone implements a 90% reimplementation of Excel in Python that would be a really useful library for stuff like this. You could do some neat stuff with dependency identification too.