Well, it depends upon what you would consider as easy, but here goes. You would need to install the Dconf-Editor from AppCenter, then do the following: Type 'ctrl-f' to search, type in 'touchpad' and keep searching until you get to this key 'org.gnome.desktop.peripherals.touchpad' You can choose enabled, disabled, or, as I do, disabled on external mouse.
Callista, I thought I'd found the answer to not having the touchpad get in the way of my ability to use Loki 0.4.1. Followed your instructions and got "disabled-on-external-mouse" set in peripherals > touchpad. My touchpad is still activated. Do you have any other ideas? Mike