In Bamboo Build server how do I prevent 2 particular plans from running at the same time?

Question

I am running Bamboo 3.4.2. I have 2 plans (among many), one scheduled and one commit triggered, that I need to prevent running at the same time as they conflict. They are in the same Project so if there is a way to only allow one Plan in a Project to run that would be entirely acceptable. I am entirely willing to commit an agent to just service that Project but I can't find a way of doing that.

Thanks, Matthew