FitNesse - Offsetting !today with a variable

Hello,

I have an issue where I am attempting to offset !today by a declared variable to verify a due date.

Example:

!define dueDateOffset {10}

|script|
|verify field | Processing Due Date | contains | !today +${dueDateOffset}|

Result:

The following script produces the result I want but does not use the variable, unfortunately I need to keep this dynamic so the variable is needed.

|script|
|verify field | Processing Due Date | contains | !today +10|

Result

How do I use a variable to offset today's date?