How do I group billable expenses onto one line item of an invoice?

How do I group billable expenses onto one line item of an invoice?

I have multiple expenses that are billable. When I create an invoice, I can add those billable expenses to the invoice. However, doing so results in each individual expense having its own line item on the invoice. Instead, I want all the billable expenses to show on one line item as "Project Expenses" with the total amount of all the billable expenses.

How do I do this?