A little more detail about what I'm thing now this is just an example because my OP was kinda confusing.
For example sake were gunna use a s363 and a s475
You would put the 475 on the manifold exhaust out of the 75 feeds the 63. Exhaust from the 63 goes to the downpipe. The air filter will be connected to the inlet of the 75. The discharge from the 75 will feed the inlet of the 63 (to be compounded). Discharge on the 63 to the intercooler. This system would utilize a WG on the manifold which stays open under low boost/drive situations driving the 63 harder for quick spool, and would close at desired boost/drive to drive the 75 harder. This system will also use a waste gage between the 75 and 63 on the interstate exhaust Pipe to prevent overspooling and high drive caused by the restriction downstream of the 75.
And my thinking in all this i guess would be it would still be a compound setup but also act like a sequential setup in its own aspect.
I don't know if this clarified my thoughts to anyone, but like i stated before it might be a god awful idea but Im always for a good technical discussion about out of the box ideas