i don’t think i read this suggestion before, but correct me if i’m wrong:
to my knowledge, it is currently not possible to edit your selection; with that i mean to extend or retract a selection by means of pulling on little two-way arrows when hovering over either side of the selection.
i thought about the possibilities for scripting this, but i think you cannot do this other than through a system of sliders and/or value input boxes, which i think would be a not so elegant way of implementing this, when compared to the (common) suggestion above.
ha! seems strange to have such a useful thing hidden away, but thanks for the tip! might be useful to create a statusbar-message when making a selection in the sample editor, which says ‘hold shift and drag to edit your selection’ or something along those lines.