.tmux: Load alternate configuration on unsupported versions

I am attempting to setup a tmux config that will work on various tmux versions. My first attempt was to load configuration conditionally in my ~/.tmux.conf file based on the tmux version, which works great but .tmux doesn’t like not being at ~/.tmux.conf … is there any way around this? Maybe adding a ~/.tmux.conf.unsupported (similar to ~/.tmux.conf.local) option that gets loaded instead of .tmux when it detects unsupported versions?