To build boost we will need load (the amount of exhaust increase much more by load than it does by revs), by revving the engine in neutral the only load we have is from the crankshaft and flywheel inertia, and that won't do that much. To build up boost in neutral we will need an anti lag system.
CFM, cubic feet per minute is a volume flow unit, this is usually measured before the compressor in a turbocharged engine. But if we instead measure it after the compressor we will find that if we turbocharge a NA engine the turbochargered one will have the same volume flow as the NA one, but its mass flow have increased due to the higher density. However, if we measure before the compressor the volume flow into the turbocharged engine is higher than for the NA engine.
To build up boost the compressor must deliver more air mass flow than the engine consumes. To maintain boost the compressor must deliver the same air mass flow as the engine consumes but a higher volume flow.