Это несколько громоздко делать вне ggplot2, но выполнимо.
plot.design(warpbreaks, axes = FALSE) # plot with no axes
axis(2) # add y as predefined by default
# manually add text in place of the label
text(1:2, par("usr")[3], labels = c("wool", "tension"), srt = 45, adj = c(1.1,1.1), xpd = TRUE)
box() # you need this to have the square around your image