[R] Lattice xyplot: same scales within one factor

[OB]

I am using R 2.8.1 and lattice to produce xyplots conditioned on
two factors. What I would like is to have the scales be free between values
of one factor, but some within. Thus, in this example,

xyplot(mpg ~ disp | factor(gear) + factor(cyl), mtcars,
        scales=list(x=list(relation="free")))

rather than having the x scales be free within a gear as well, I want it to
be the same for the gear, but free between cyl (and thus only have x scales
below the bottom panels with no scales or white space in the middle between
panels).

Any help would be greatly appreciated!

-Orion