[R-sig-ME] lme: several slopes, same variance, no correlation

[Ben Pelzer]

Dear list,

I am trying to fit a model with 4 crossed (no hierarchy) random effects 
which all four are considered to be independent draws from one and the 
same normal distribution. So, all four have the same variance and the 
correlations are zero. In lmer I could specify something like:

lmer(y ~ 1+ (x1|id1) + (x2|id2) + (x3|id3) + (id4|id4))

but then four different variances would be estimated and also all the 
covariances.

Would it be possible to estimate such a model in lme, where one can have 
all kinds of correlation structures? Thanks for any help!

Ben.