You should understand (although many people do not) that boxplots show neither means nor standard deviations and they don't display the interquartile range except by accident. You could use the same strategy to "annotate a boxplot". (Using the data construction of the prior question.)
x<-data.frame(A=c(1:10), B=c(1:10)+rnorm(10))
xx<-stack(x) # restructures data for stripchart function
with( xx, boxplot(values~ind))
apply(x,1,lines, col="blue")
apply(x,1,points, col="red")
This could probably be improved for more general use by using smaller points and having the colors be transparent, if there were large numbers of cases.