Entity Framework 6.0 code-first - adding an index to the discriminator column

Question

I've encountered a very specific problem regarding code-first EF 6.0, and I don't believe what I'm trying to accomplish is supported by EF 6. At a high level, I'd like to create an index on a table over three columns, and I'd like this index to include the Discriminator column.

Unfortunately, there is not a way to access shadow properties (like the Discriminator) via FluentAPI in EF6 (this functionality is only present in EF Core).

Does anyone have any experience with manually making changes to the schema outside of the code-first approach, and then bringing the code-first model up to speed with manual SQL Server updates?

Or do you have any suggestions to implement this index that do not involve adding additional columns to my code-first schema?

I've looked into manually creating an index on SQL Server for the three columns, but doing so will throw the code-first model out of sync with the DB model, as no entry in the Migrations table would be made for the manually created index.

I find it very strange that the code-first framework prohibits me from accessing data that is stored in my database. I understand that the Discriminator is used behind the scenes by EF when implementing the table per hierarchy schema design, I just find it unnecessarily prohibitive to disallow access to columns within my database.

Any suggestions are welcome!