Hi randavidovitz,
Thanks for your comments. You are correct in that there isn't a very good solution to this with EF at the moment. We have an item filed in CodePlex to track this (http://entityframework.codeplex.com/workitem/86) and there is also a request for this on our User Voice site (http://data.uservoice.com/forums/72025-entity-framework-feature-suggestions/suggestions/1249289-include-property-of-derived-classes). I encourage you to vote in both places if you haven't done so already. Unfortunately it is very unlikely at this point that we will be able to fit this into EF6, but we are aware that this is a highly requested feature and do hope to add support in a future release.
Thanks,
Arthur