[Yutaka Emura]

If you have EmEditor Professional, you can write a macro like this (JavaScript):

var bEmpty = false;

	if( document.selection.IsEmpty ){

	    editor.ExecuteCommandByID(4154);  // Select line if not selected

	    bEmpty = true;

	}

	editor.ExecuteCommandByID(4371);   // Comment.  Use 4372 for Uncomment.

	if( bEmpty ){

	    document.selection.Collapse();

	}

This macro can comment selected lines if selected, or comment the current line if not selected.

Then you can customize menus to insert this macro to anywhere you would like.