Is there a way in ggplot2::geom_boxplot() to replace the lines between the IQR and the whiskers using a second rectangle? Here is an example of the visual I am trying to achieve:

source : Hydroclimatic Atlas of Southern Québec,

Or, without the borders:

ggplot(x, aes(species, V3))  
  geom_crossbar(aes(ymin=V1,ymax=V5, fill=species), alpha=0.5, size=0)  
  geom_crossbar(aes(ymin=V2,ymax=V4, fill=species), size=0)  
  geom_crossbar(aes(ymin=V3,ymax=V3, fill=species))