Establishing Control %/Hold-Outs

Hi,

This may seem like a really silly question, but I am completely new to Marketo and lacking in sufficient training. In my previous system, when running a nurturing campaign, we were able to establish a certain % of records/leads to be mailed/emailed, while holding-out or creating a control group who would not get the nurture piece (say 80/20). Is something like this possible in Marketo? I've seen some discussion on A/B testing, but that seems to be with a set group of leads/people, not a continuing cadence of incoming leads.

Thanks!!

Lindsay Marshall