How is the clamp necessary in your picture at all? It looks as though the slide is just resting on a horizontal partition?
In terms of fore/aft alignment- you can mark a consistent line for the first screw, and pre drill at whatever height you want.
When I have to place a higher slide in the field, I install that front screw and just hold the slide up in the back so it measures a consistent parallel distance from the cabinet floor. Begin the pre drill with a Vix bit and secure. I like to keep at least two drills handy- one for the predrill, and another one to drive screws. It's decently fast, and entirely accurate. (I've tried the Kreg jig, but have never been happy with the results.)
When stacking drawers multiple times at the same height, we use scrap ply to make consistent supports for installing the slides in the cabinet after it's been assembled. You do the top slide first, then a shorter piece for the next lower, and so on.
Does that help?