Naming Conventions For Partial Class Files

I'm generating the bulk of my ASP.NET MVC scaffolding code. All generated files are partial classes which use standard naming conventions. For example, my employee controller file is named EmployeeController.cs. If I wish to extend the EmployeeController with custom, non-generated logic, I create a second partial class file named EmployeeControllerCustom.cs. I separate the custom and generated logic into two different files so the next time I generate the EmployeeController my custom changes aren't overwritten. Adding the "Custom" suffix to the file name seems reasonable to me, but is there a more established partial class file naming convention which I should be following?

I use . separation - for example EmployeeController.SomeSpecialBehaviour.cs. I also link it into the project tree via "dependentUpon" or whatever it is in the csproj, so that it nests under the file (in solution explorer) neatly. You have to do that by hand (edit the csproj) or with an addin, though; for example:

<Compile Include="Subfolder/Program.cs" />
<Compile Include="Subfolder/Program.Foo.cs">
  <DependentUpon>Program.cs</DependentUpon> <!-- Note that I do not reference the subfolder here -->
</Compile>

appears as:

• Subfolder
  • Program.cs
    • Program.Foo.cs

UPDATE / DISCLAIMER: On 2018 someone edited Marc Gravell♦'s answer (the one accepted above) to include a subfolder in his example. And how to handle the case of having a subfolder is the main point of this answer.

Without that disclaimer you probably wouldn't understand why this answer exists and why it has so many votes.

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To add to Marc Gravell♦'s answer, I had a situation with files in a subfolder and the DependentUpon node being ignored. The short of it is that in such a case it my xml had to be:

<Compile Include="foo\bar.cs" />
<Compile Include="foo\bar.baz.cs">
    <DependentUpon>bar.cs</DependentUpon>  <!-- Note that I do not reference the subfolder here -->
</Compile>

I hope this helps someone :)