Get variance components for each level of a random factor in lme4

Question

Using the sleepstudy dataset as an example, if I run the following code I can obtain the variance component for the random factor in this model, 'Subject'.

data("sleepstudy")
model<-lmer(Reaction~Days + (1|Subject), data=sleepstudy)
print(VarCorr(model),comp=c("Variance"))
 #Groups   Name        Variance
 #Subject  (Intercept) 1378.18 
 #Residual              960.46

But what if I wanted to know the variance attributable to Subject 308 vs Subject 370 etc? Is this possible?

I think I see here that it is possible in nlme, but is there an lme4 solution?