There has been a discussion before about excel formulas. It might be possible to do that via python code. You would have to load the excel file containing the formulas, run the code and save it again.
I have not yet found a function for that in the powerful Python package openpyxl.
You might also want to check out this thread although it would only work to recalculate the formulas prior to loading the data into KNIME. You would not be able to save the excel file with the formulas.