How do folks organize and download AssetBundles for different platforms?

Hi, I have a multiplatform application, so I need to build the AssetBundles for each platform, and then I store them on my website, in a platform-specific directory, based on the buildTarget. So, the iOS AssetBundle goes into ./iOS, and StandaloneWindows into ./StandaloneWindows and so on. So, when the Player needs to download the AssetBundle, it needs to construct the URL at runtime. But, the buildTarget is not available at runtime. How do people deal with this sort of thing? It seems like such a basic problem, but I don't see a whole lot of people talking about it, so I must be missing something.