Hi Simon thanks for posting in the Lucidchart Community! Unfortunately what you are trying to do is not currently supported in Lucidchart. However we're always looking for ways to improve Lucidchart and your feedback is the best way for us to do that. Would you mind adding your idea to our feature request form? Ideas submitted to this form are passed on to the product development team for their consideration.

Thanks for your request and I apologize for any inconvenience this causes you.

For more information on formulas in Lucidchart please take a look at the How to Use Formulas article in our Help Center.