AutoCAD Inventor :: Calculate Total Length Of Multiple Doors On Single Machine

I use flat piano hinges on doors for many of the machines we build. I would like to be able to calculate the total length of multiple doors on a single machine. We buy these hinges so it needs to go on a buy out parts list.

So here is my problem:

To make it a useable hinge I build an assembly from two hinge halves.

This allows me to check for interference within the machine when the door gets opened.

I set the BOM structure of the assembly to purchased so it shows up on my buy out list.

Both halves of the hinge are set to normal.

There are hinges of different lengths on the same machine.

I can link a parameter of one of the halves to the assembly to show length of the hinge but I cannot set the BOM base qty on the assembly to that parameter so Inventor can add up the lengths.

When I group the items in a buyout parts list the result is  "0." The individual assemblies show the correct length because I use the "length" parameter that is linked for the QTY in the parts list. But I cant "add" the lengths and have a total whe I group them.

I need to have mixed units in this list. Some things are bought as Each and these hinges are bought in length.