Has anyone been able to add a box to their statements for amount of late fees assessed? If so, how?

I'm envisioning something like the below examples:

or

I was thinking of adding a custom field to the customer record near balance/days overdue/etc. for "Finance Charges" and have that update either by a formula or script that calculates that value, but that is a bit more complex than I have done before.

If anyone has achieved this before, please let me know how you did it!