Modifying an X-Y table

Well, today there was one of those neat tool sales they hold out in
rural area. Homier is a popular company for these, though today's was
Cummins Tools.

While I was there, I found a fun little toy. Its castings are a bit
rough, but it's a cross-slide drill press vise, essentially a 4x6 inch
X-Y table with a vise on top. Needless to say, my mind immediately
turned to its possibilities as a low cost CNC platform. And, for
$19.99, I couldn't turn it down! It should make a good complement to my
much larger (but potentially less accurate) wood router. Large wooden
parts, small but accurate metal parts? I could make almost anything! ;-)

Yes, you read it right, $19.99 is its full retail price! Dovetail
slides, and a built in facility for shimming it to minimize play...not
too shabby for the price. It seems reasonably well designed.

http://www.cumminstools.com/browse.cfm/4,92.htm

Well, like I said, it's a bit rough in person, but it has potential.
Acme lead screws and nuts, too -- but unfortunately there's some
backlash in the system. Enough that I want to do something about it.
So, here's my question.

Is it possible to modify *existing* nuts to display less backlash?
Perhaps by injecting some sort of polymer into them, or something? You
see, the nuts are part of the casting, as far as I can tell, so there's
no way to remove, modify, or replace them. And, since it's almost
definitely of Chinese origin, the ACME lead scrws are probably of metric
size, which is even harder to find here in the States. I'd rather use
the existing stuff, and just "improve" it, if it's at all possible.
Since it's got such limited travel, as is, I'd like to avoid *adding*
another nut, for example...that would cut down on the capacity of the
table, though that might be the easiest way to make the modification.

Anyone have any good ideas?

-- Chuck Knight