Summon it, and just don't fly in flying areas. You could otherwise summon it in BG's, and WOD and it (obviously) won't fly.
And can we make the new RaF mount a flying mount? It loads as a ground mount, even though it can fly.
HB staff is fairly adamant about the different between ground mount and flying mount as I've seen in other threads.. the issue is not all mounts are "flying" mounts that can walk on the ground (ie if you use a frostwyrm in WoD, yes it walks on the ground but it is 100% a flying mount). There are plenty of newer mounts in the game (specifically say the Grinning Reaver) that are built around being both. In a no-fly zone they act only as a ground mount. The tooltips even specify that the capabilities of the mount change based off the current location. There's no issues with meshes, or pathing, or anything like that with these mounts. They need to be added to the ground mount selection, or at least be available if you hit "choose random mount."