Is there some way to add a single fee to total order amount? I spent the last five hours trying to accomplish this.

-There is a way to add a fee to each product, or product type
-There is a way to add a single percentage fee over the total order amount

But there seems to be NO way to add a (fixed) fee to the total order amount, as there is no rule like 'Add an amount to the total order balance'. I saw there are more people who questioned this, but they all don't get the answer they need.

Note that I want to be the fee a price component type (like tax, fee, etc.), so it appears at the review pane in the same way the tax is displayed... not as a line item.

Is there a way to accomplish this wit an additional module I overlooked, or has it to be done with a custom module or something like that?