[blevs]

You can configure your local tmux to have a key press send the prefix command to a remote tmux with a single keypress.

For example, to bind C-a to control the remote session:

   bind-key -n C-a send-prefix

[sys_64738]

Binding isn't an option as only defaults are available on target machines (can't save .screenrc file). There can be thousands of target machines so binding doesn't scale.

[blevs]

I'm sorry I wasn't clear. This would be a binding in your local tmux configuration that sends the prefix command to whatever is in your current pane, allowing you to have a key act as a 'remote prefix' button.

I agree that bindings still don't scale incredibly well depending on the number of host machines you need to ssh from. I think your screen workaround is a pretty neat solution.