You're just looking to change the aspect ratio? I don't think there's a built in way, the height/width appear to be hardcoded in include/tic80.h. It doesn't look like it would be that hard to swap them and recompile, although I'm not sure if the UI could adapt.
Not a proper suggestion, but I remember for some crt games the suggestion was to turn the display on it's side. A number of monitors also have stands that rotation - you'd need to