There are a few shortcuts provided for quick selection of which particular variations you are editing. The vertical bar to the left of the 32 variation buttons selects (and with a second click deselects) all enabled variations. Double-clicking on a variation will "solo" it (only select that variation). Double-clicking again will "unsolo" it, reverting to the previously pressed buttons.
If you are using linear wave files, a shortcut is provided to avoid needing to work directly with the 32 variation buttons at all. From the File menu, choose Import>Wave File(s) as Segment Variation(s)…. From the dialog that appears, choose all of the wave files that you want to be variations in your Segment. A clock-time Segment is automatically generated, with a length of the longest wave file you chose and using one variation per wave file. You'll notice that in this case, all of the empty variations (unless of course no variations are empty) are automatically disabled.