I have a master assembly which contains several components, one of which is a large sub-assembly (lets call it "B").

Within the master assembly I can make configurations where some of these components may be suppressed, including B.

However, I can not create a configuration where B is unsuppressed, but some of its components are suppressed.

In other words, in a top level assembly it seems that as far as configurations are concerned you can only toggle suppression states (selectively per configuration) on top level components, no deeper. I hope I have explained this so it makes sense. 

Is this true?

Yes, I know I can create configurations within B and then use those configurations within my master assembly but I would prefer not to if I can avoid it.

Also, I am aware of display states, but as far as I know display states can not suppress/unsupress parts.

I need the parts to be suppress/unsuppressed as opposed to hidden so that it give correct BOM quantities in the various configurations.

thanks for any pointers