I would create a WBS code called Addon or something like that.

Mark all the bid items that are to have Addon = 1 as such and Addon = 2 as such  (in your case addon 2 would be the items you are excluding - but woudl be setup for future use)

You can create a spreadsheet sort for the Addon WBS to quickly assign these values in the future

Then create two Addons Total type with the range assigned.   WBS Addon 1 with the range of 1 to 1 mark to pick up the 1st range of bid items and WBS addon 2 with the range or 2 to 2 to pick up the 2nd range of bid items (you could skip this step because you were going to exclude these bid items from the calculation)