Yeah, I think you're right that it only allows for one - [this seems to confirm](https://github.com/umbraco/Umbraco-CMS/blob/e42149e8d99d507dc26d34837475830b79c6eb1d/src/Umbraco.Core/Models/PublishedContent/PublishedPropertyType.cs#L189-L198).  Thanks for all your help!  Hopefully we can get a cooler way to handle all this soon :)