[NTG-context] installing two ConTeXt trees

I would like to install two ConTeXt trees on my laptop, one for work in progress and another for testing, and to run them using TeXShop (if that is feasible). Are there any instructions for this? I have searched the wiki and TeXShop help files but have not seen anything that indicates how to do this. I currently have a system-wide installation of the ConTeXt standalone. Alan