To include an external hire from Upwork or another agency in the payment sheet, fill in their details in the corresponding row. In the 'Creative Name' column, list the external agency or platform name (e.g., Upwork), and select the relevant level (e.g., Emerging, Senior, or Pro) based on the position they are filling. Also, be sure to specify the duration of their engagement, including start and end dates if it's a temporary arrangement.