heteroscedasticity

Hi,

Suppose may data consist of groups (which also define the levels for 
random effects), which show group-wise heteroscedasticity, that is for 
some groups the variance of residuals is larger than for the others.  
Based on specific knowledge of the data and the problem this even makes 
perfect sense and is actually a good sign. Technically however it's not 
good of course, to put it mildly.
Is there a way in lme4 to handle heteroscedasticity (with known grouping 
for the different variances) ?
Any suggestions ?

thanks
Thomas