Bindable property with options in drop down list?

I created a custom control (call it MyWidget) in a C# web control
library. MyWidget has a SqlDataSource property:

public abstract class MyWidget : WebControl
{
// .... snipped

private SqlDataSource myds;

[Bindable(true)]
[Category("_Custom")]
public SqlDataSource DataSource
{
get { return myds; }
set { myds = value; }
}
}

In the VS.NET designer's property window, I want a list of available/
existing SqlDataSource's the programmer can pick from in a drop down
list box. I'd also like it if the property can't be null. How can I do
this?
thanks,
Tombow