R ggplot2 facet_grid "hierarchical" formatting with 3 variables or more

Question

I'm trying to get a nice show if there are several variables in one dimension of mine facet_grid, so that instead of repeating the name of all the variables for each column (or row), I have a combined box above the sub-boxes, Taking a specific example with the default data set from R (based on R Cookbook):

library(reshape2)
sp <- ggplot(tips, aes(x=total_bill, y=tip/total_bill)) +
      geom_point(shape=1) +
      facet_grid(smoker ~ sex+day)
sp

This returns something like the top of this drawing , with Female / Male repeating at the top of each column. Is there a way (in R) instead of merging all the gender blocks to get something like the bottom of the figure I downloaded? (I did it with Gimp, of course, this is not ideal)

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