You can do this by creating the editor yourself rather than allowing TypeDescriptor to do it as follows.

First, shadow the property you care about in your designer:

protected override void PreFilterProperties( IDictionaryProperties props ) 
{ 
  PropertyDescriptor basePD = props[ "MyProperty" ]; 
  props[ "MyProperty" ] = new EditorPropertyDescriptor( basePD ); 
} 

Second, create a property descriptor that wraps the original descriptor:

private class EditorPropertyDescriptor : PropertyDescriptor 
{ 
  private PropertyDescriptor basePD; 

  public EditorPropertyDescriptor( PropertyDescriptor base ) 
  { 
    basePD = base; 
  } 

  // now, for each property and method, just delegate to the base... 
  public override TypeConverter Converter 
  { get { return basePD.Converter; } }
 
  public override bool CanResetValue( object comp ) 
  { return basePD.CanResetValue( comp ); } 

Third, create your editor by hand when it's asked for:

  public override object GetEditor( Type editorBaseType ) 
  { 
    if ( editorBaseType == typeof( UITypeEditor ) ) 
      return new MyEditor( param1, param2, param3 ); 
    return basePD.GetEditor( editorBaseType ); 
  } 

}

Shawn Burke, Microsoft