Excruciatingly difficult. M2s have 'dynamic skins' of sorts, which the client does not know how to deal with unless they're bound to a player. This is why all the items have no skin (are white). This can be surpassed by making a new m2 object for every item in the game, but that's... a lot of files. Like, a LOT of files. The issue isn't time, I can make them in an afternoon, the issue is that it's hundreds of thosands of files, meaning another 10+ CDN servers. Or a single untouchable, statically spawned items server, which may lead to slow load times for the items.
It will require a considerable amount of reverse engineering to deal with effectively using existing files--but it's not impossible. And it's something I realy, really want to do, the ability to spawn items for the purposes of displays, mannequins, warfronts, etc.