There IS a way to accomplish what you want. Use the power of excel in your BOM.
Edit Your BOM template file.
Add a column for UOM (Unit of measure)
Add a column for QTY (Quantity entered)
Use 'Insert/Name/Define' in Excel to read custom props referencing UOM and QTY.
Naturally, your parts will need added custom properties for UOM and QTY for where you want to see a special value.
Add a column for QTY (Quantity calculated). Excel will fill this out, so you don't need to add a custom prop reference.
Assume your column 'B' is the standard SWX 'quantity' as measured by SolidWorks, column 'C' is for 'UOM', column 'D' is for quantity entered, and column 'E' is for quantity calculated. Use a formula in column 'E' such as:
=IF(ISTEXT(C4),(CONCATENATE((D4*B4)," ",C4)),B4)
This formula says:
If text is entered in UOM,
then fill in the 'Quantity Calculated' as
the SWX measured quantity multiplied by
the 'Quantity Entered' value
and add on the UOM as a suffix.
Otherwise, just use the SWX measured quantity value.
Copy the formula down for as many rows as your BOM might use. Then hide columns 'B', 'C', and 'D', leaving the 'quantity calculated' column showing.
To use it, you would need to populate the custom property in the part for UOM and QTY. For example, if your deck planks as modeled were 10 feet long, put FT in the UOM field, and 10 in the QTY field. Now if you use your new template for your BOM, it should fill in '10 FT' in the 'quantity calculated' column. By the way, the header can still just be 'QTY' - SolidWorks doesn't care about the header, only the name used in the 'Insert/Name/Define' box.
I hope that all makes some sense!
D Hinners