Results from multiple entities

Hi, I've searched a lot and can't seem to find an answer to this. I'd like to have a calendar that displays events coming from multiple entities (nodes and entityform results in my case). There is no direct relation between the two entities, both use date fields. I can make a calendar based on nodes, I can make a calendar based on entityforms. But I can't seem to find a way to combine the view.

The only 'hack' I was able to find is here. But I think combining multiple queries in one calendar is a legitimate use case. I can images pulling dates into a calendar from nodes and taxonomies and so on.
Thanks