Is it possible to have "dummy" parts inside of an assembly?

Is it possible to have "dummy" parts inside of an assembly that are used just for layout purposes?  I thought about using the envelope feature, but it looks like you have to create envelopes ahead of time.  I already have an assembly with the parts in it.   I dont want these parts to show up in my BOM or interference detection.

Is this possible?

Thanks.

SolidworksAssemblies