Adam, following your comment above ("I wanted the empty plot to serve as filler in a multiplot (mfrow) plot."), what you actually want is the mfg option
par(mfg=c(row,column))
- which controls where you want to put the next plot. For instance, to put a plot in the middle of a 3x3 multiplot, do
par(mfrow=c(3,3))
par(mfg=c(2,2))
plot(rnorm(10))