Question about lrandom effects specification in lme4

Folks:

Suppose I have 3 random effects, A,B, and C. Using the older lme() function
(in nlme) it was possible (using the pdMat classes) to specify that they are
uncorrelated with identical variances. Is it possible to do this with lmer?
My understanding is that if I specify them as

lmer( y ~ ... + (A|Grp) + (B|Grp) + (C|Grp))

then they are uncorrelated but have different variances.

Motivation: I'd like to use lmer instead of lme for fitting smoothing
splines to longitudinal data.

Cheers,
Bert Gunter
Genentech