Writing in hemiola

I write frequently in two simultaneous time signatures: 6/8 and 3/4. I would like to be able to make my eigth note groupings reflect the time signature they are in , which is different for different instruments in the same measure. I would like to be able to regroup my eighth notes to two groups of three while still in 3/4. Is this already possible and I am just missing it?
(Melody in 3/4 while rhythm plays in 6/8)