How to specify the shape of results with WebApi2, OData with $expand

Question

I have a problem executing my AutoMapper mappings when using OData with specific $select or $expand values.

Using the WebApi Action:

    public IQueryable<BookInRequestDto> Get(ODataQueryOptions<BookInRequest> query)
    {
        var results = query.ApplyTo(_context.BookInRequests) as IQueryable<BookInRequest>;
        var mappedResults = Mapper.Map<IQueryable<BookInRequest>, IQueryable<BookInRequestDto>>(results);
        return mappedResults;
    }

When I query: api/Get, I get an appropriate response, but a Document's Properties is set to null response containing documents properties set to null.

When I query: api/Get?$expand=Documents/Properties, the response is an empty array.

As I understand, this is because Select/Expand changes the shape of the response, so it no longer matches an IQueryable of BookInRequest, and instead returns an IQueryable.

I'm happy to return that, except I need to be able to apply the AutoMapper Mappings. Is there anything that can be done to enforce the shape of the query results?

I have the following entities:

public class BookInRequest {
    //...
    public virtual ICollection<BookInDocument> Documents { get; set; }
}

public class BookInDocument {
    public ICollection<BookInDocumentProperty> Properties { get; set; }     
}

With Corresponding DTO's that are pretty much identical, except for the BookInDocumentDto:

public class BookInDocumentDto {
    public dynamic Properties { get; set; }
}

My Mapping definition is as follows:

Mapper.CreateMap<BookInRequest, BookInRequestDto>();
Mapper.CreateMap<BookInDocument, BookInDocumentDto>()
        .ForMember(x => x.Properties, 
          y => y.MapFrom(z => 
                   DynamicHelpers.PropertiesAsDynamic(z.Properties)));