If you get an extension....now let me think who might be able to do that for you
, you will be able to use less weight to balance it, but to be able to move the scope lower along the dovetail you will need to make the mirror end heavier. The best way to do that may be to put a heavy weight (magnets are a good choice for a start) on the mirror end of the tube...but...if you put the tube too low it may catch on the leg of the tripod as it moves around. You could test this by releasing the clutches and checking you can swing it around without hitting. Of course, if you put more weight on the tube, you will need even more weight on the bar to balance it, but if the bar is longer, you can move the weight further down the bar!
Hope that is as clear as mud!