[BioC] Group samples on heatmap?

[Michael Imbeault]

Is there a way to group samples and display them on an heatmap? Im using 
the simpleaffy package to analyze some Affymetrix data - we have 12 
chips, 6 from each donor (A and B) at different time points / treatments.

Im using hmap.pc to build an heatmap out of a filtered paircomp object, 
but would want to display the mean of the 2 donors for each treatment / 
time pair (so 6 samples total) instead of each chip on the heatmap.

Can this be done?