Norms GXP spoiler is held on with 3M tape at various points in the front, and the ends wrap around the front of the wheel well and then screws into a wheel liner attachment point. But the GXP center section does provide additional support for it to be held on. I suppose it could work without it, but I'm just not sure for how long.you can see at the bottom where I have the air dam piece stitched to the honeycomb insert. The Intercooler is one of the aftermarket ones so it is a touch bigger.
If you look closely at the ends you can see how they wrap inside the wheel well, there's either one or two holes in the ends that line up with the wheel well liner attachment bolts. But even when the spoiler is attached properly you still run the risk of it being ripped off by parking stops, speed bumps, high angled entry and exit ramps, etc. Especially if the car is also lowered with lowering springs or adjustable coilovers.
Point being it really would be in your best interest to replace your GXP fascia.