There LOTS of ways to twincharge, seperate inlets are the most common, and of course they do need some form of bypass, as would supercharger first, but the simplest and most effective (esp as supercharger is never a restriction) is compound charged with turbo blowing into charger.

BIG distadvantage to this setup is charge temps, but providing charger is pre intercooler, thats easy solved.

Lots of twincharged cars around these days, the CooperS twincharged conversions are done like I mention, as are most others that work properly.

Countless other types, but most are much fancier and dont work well, hence why they not popular.

Not so sure about the G60 idea, their charger work a little different, and no idea how well theyd take to having pressure in their inlet.

Golf GT system id like to see, the VW diagrams show supercharger blowing into turbo, but wether its really like that, who knows, but if it is youd deffo need either a bypass or cleverly sized turbo+SC.
cant think of a reason theyd do it that way tho, unless it for economy/reliability reasons that i cant think of.