Is it possible to add a task item that represents a flat fee for a project.  I currently create projects for each client where I perform weekly services.  They are charged per hour of service but I have the need to include flat fees (e.g. parking or materials fees) per work day. 

There does not seem to be an easy way to incorporate this unless I manually add invoice line items at the end of the month.  Currently this relies on me keeping separate notes of what line item charges I need to include into the monthly invoice at the end of the month.  Is there a better way of tackling this?