You can receive mouse and mouseup information in Vanilla by using [receive .x55dca8289140], where ".x55dca8289140" is a hexadecimal ID unique to the given canvas. However, the only way I know of retrieving that ID is using [hcs/canvasname], which is back to using externals.
Good information, thanks Liam! Does the Canvas ID change when re-opening the patch or will it remain the same "forever"?