How else?... easy.. considering it won't be a "real" helicopter & just a fabricated prop piece that won't weigh that much, those 3 supports on the side of the building would be enough considering a steel rod would connect to each point & then extend through the helicopter (none of which would be visible to guests). Its really not that complicated.
The main problem with this whole helicopter "idea" is that the facades are not exactly to scale, so a big helicopter is going to end up looking ridiculous "crashing" into such a small façade. But again, the buildings in the concept art don't even match the new (or old) Baker st facades, so I guess the facades not being to scale matter that much.