What's the best way to bring the dividers down flush with the back?

Maybe a flush-cut saw? Granted he'd have to buy something new, but
even a nice one (i.e. Veritas by Lee Valley) isn't too expensive
($16-19, see below for link). It would take a while to go through any
significant distance of 3/4" ply, but it might be easier than
re-building the cabinets.
Andy
http://www.leevalley.com/wood/page.a...28&cat=1,42884