1. Manual override in BOM/parts list
2.
Prep work (only do once)
a. make a copy of this part, name it "part phantom" or something meaningful
b. make the default BOM structure setting of "part phantom.ipt" to "Phantom" ***
c. make an assembly, insert one "real" version of this part, and one "phantom" version, name this assembly "part pair.iam" or something meaningful to you
d. make the default BOM structure of "part pair.iam" to "Phantom"
Project work (do every time you need these parts)
a. insert "part pair.iam" into your main assembly
b. make "part pair.iam" flexible
c. constrain the parts as needed and work as you normally do
Result: everything works per normal, except only half of these parts will show up in your BOM.
***Setting the BOM structure of a part to "Phantom" will keep it out of your BOM. It will still display normally, and still factor in mass calculations as normal.