Question about a user control derived from DropDownList

[Big Daddy]

I posted this in a different group last week with no responses, so I'll
try here.

I have a simple control that is in a CS file (not ASCX). It is derived
from DropDownList like this

public class FiltersDropDown : DropDownList
{
....

}

It overrides a couple of functions. I want to include this
FiltersDropDown control in an ASPX file. I know how to use the "@
register" directive to include an ASCX file, but it doesn't seem to
work when the control is defined in a CS file. If I put the CS file in
a library (DLL) I am able to access it, but I don't want to put it in a
library; I just want to include it in the web site like a regular file.
I have tried putting it in the root directory of the website, a custom
subdirectory, or the app_code subdirectory, without any success. Any
ideas? I am using ASP.NET 2.0

Thanks in advance,
John