This is a problem with the DAO (data access object), today there is no automatically way to do this using entity framework (standard of mvc 5 and asp.net identity).
Some suggestions:
1) Its easy create or override and use the "RoleManager" and "UserManager" with your own rules.
2) You can encapsulate the data access, using something like a proxy or a wrapper to get the data from entity framework
The only thing you definitely will not be able to overcome (if you want to use) is the "custom mapping", I mean... The collection property of Employer always will load the data based on mapping configuration, and the mapping configuration it is a little bit limited (is not support a custom clauses, like a where in the relation).