[R-sig-Geo] spplot how to control variable scale with colorkey()

[Paulo Eduardo Cardoso]

While plotting with spplot, the legend space is reflecting the scale
of the variable.

eg, by dping something like this:
spplot(...,
colorkey = list(at = c(0, 5, 10, 20, 50,100), labels = c("0", "< 5",
"[5, 10)", "[10, 20)",
 "[20, 50)", ">= 50"), space="bottom"))

spaces between each colour interval will be proportional to the scale
of this particular variable.

Can one control this, forcing a equal interval space to the legend at colorkey?

Paulo