I think that this is possible to do. Sad that you won't be getting much light through the sunroof when you have the roofrack in place but that is about the only down side that I can see. You could also consider trailers to tow instead which would be an alternative way to transport things.
Hey man, yeah you can get a Thule brand style one for certain, I own a 14' GT with Panoramic roof and was going to get one to use when I want to move my kayak to the water. I've also seen another Elantra GT with a panoramic roof around my area with a roof rack for a bike and kayak on it too.
Here is another one here for far cheaper than Thule's though, just don't try opening the sunroof with it, haha.