Imagine air flow to be simular to the flow of water.
Then think of boost as a messure of restriction to flow.
The other way to think of it is - there's only so much water you can flow out of a 3/4 inch hose at 1 bar of pressure. But if you reduce the restriction and use a 2 inch hose at 1 bar then you'll flow a heap more water.
Remember that the restriction isn't always the pipe size, it could be intercooler design, end tank design, head ports/valve design.. Heaps of different things.
So, yepp, to increase flow without increasing boost you just need to reduce the restriction.
I better go now, my brain hurts
J