You don't really get entitytokens, the trick is to create them yourself. Suppose the reason why you think you can only get them for IData types is because it has a Extension Method that makes it easy, but there is no magic going on there.
Digging through some more code i ended up in the class AssociatedDataElementProviderHelper and here there is a line of code that shows how to correctly create a AssociatedDataElementProviderHelperEntityToken. As you can see you basically only need the PageId and the Interface Type of the Folder Data.
Digging through some more code i ended up in the class AssociatedDataElementProviderHelper and here there is a line of code that shows how to correctly create a AssociatedDataElementProviderHelperEntityToken. As you can see you basically only need the PageId and the Interface Type of the Folder Data.
return new AssociatedDataElementProviderHelperEntityToken(
TypeManager.SerializeType(typeof (IPage)),
_elementProviderContext.ProviderName,
pageId.ToString(),
TypeManager.SerializeType(interfaceType));