Can't compile ASP.NET 5 Web API when adding XML support

I'm trying to figure out how ASP.NET 5 Web API supports Content Negotiation. In order to support XML (in addition to the default JSON support), according to another answer here on Stack Overflow, I need to add that support from an optional NuGet package.

Things have changed a bit since that answer, but I pulled down the Microsoft.AspNet.Mvc.Xml package and edited my Startup.cs file:

public void ConfigureServices(IServiceCollection services)
{
    // Add framework services.
    services.AddMvc().AddMvcOptions(options =>
    {
        options.InputFormatters.Add(new XmlSerializerInputFormatter());
    });
}

This, however, doesn't compile:

The type 'InputFormatter' is defined in an assembly that is not referenced. You must add a reference to assembly 'Microsoft.AspNet.Mvc.Core, Version=6.0.0.0, Culture=neutral, PublicKeyToken=null'.

Here are the full compilation error messages:

1>C:\Users\mark\Desktop\WebApplication1\src\WebApplication1\Startup.cs(33,17,33,44): DNX 4.5.1 error CS0012: The type 'InputFormatter' is defined in an assembly that is not referenced. You must add a reference to assembly 'Microsoft.AspNet.Mvc.Core, Version=6.0.0.0, Culture=neutral, PublicKeyToken=null'.
1>C:\Users\mark\Desktop\WebApplication1\src\WebApplication1\Startup.cs(33,45,33,78): DNX 4.5.1 error CS1503: Argument 1: cannot convert from 'Microsoft.AspNet.Mvc.Xml.XmlSerializerInputFormatter' to 'Microsoft.AspNet.Mvc.Formatters.IInputFormatter'
1>C:\Users\mark\Desktop\WebApplication1\src\WebApplication1\Startup.cs(33,17,33,44): DNX Core 5.0 error CS0012: The type 'InputFormatter' is defined in an assembly that is not referenced. You must add a reference to assembly 'Microsoft.AspNet.Mvc.Core, Version=6.0.0.0, Culture=neutral, PublicKeyToken=null'.
1>C:\Users\mark\Desktop\WebApplication1\src\WebApplication1\Startup.cs(33,45,33,78): DNX Core 5.0 error CS1503: Argument 1: cannot convert from 'Microsoft.AspNet.Mvc.Xml.XmlSerializerInputFormatter' to 'Microsoft.AspNet.Mvc.Formatters.IInputFormatter'

The error message seems fairly clear, but the project already includes Microsoft.AspNet.Mvc.Core, although not quite in the desired version:

Id                                  Versions         
--                                  --------         
Microsoft.AspNet.IISPlatformHandler {1.0.0-rc1-final}
Microsoft.AspNet.Mvc                {6.0.0-rc1-final}
Microsoft.AspNet.Mvc.Core           {6.0.0-rc1-final}
Microsoft.AspNet.Mvc.Xml            {6.0.0-beta5}    
Microsoft.AspNet.Server.Kestrel     {1.0.0-rc1-final}
Microsoft.AspNet.StaticFiles        {1.0.0-rc1-final}
Microsoft.Extensions.Configurati... {1.0.0-rc1-final}
Microsoft.Extensions.Configurati... {1.0.0-rc1-final}
Microsoft.Extensions.Logging        {1.0.0-rc1-final}
Microsoft.Extensions.Logging.Con... {1.0.0-rc1-final}
Microsoft.Extensions.Logging.Debug  {1.0.0-rc1-final}

As I'm writing this, ASP.NET 5 is only available in a Release Candidate version, so the above packages are the most recent available.

Clearly, Microsoft.AspNet.Mvc.Core 6.0.0.0 isn't available. In a normal .NET project, I'd attempt to solve this issue with a binding redirect, but since this is ASP.NET 5, that's apparently no longer the way to do things.

How can I make my code compile?