A general invoice can be used for miscellaneous services. To setup a service for a General Invoice, select Template 27.
Be sure to use 'Flat' as the UOS. Keep in mind, the name of the service will be displayed on the Invoice report as the item being invoiced. And the 'Special Instructions' field on the Authorization will be displayed on the invoice as well.
In order to add any additional report or attachments, this must be done at the time of invoicing. There is no "Time Tracker" data that is entered for Template 27.