This is a theoretical solution but I don’t think it would work as described because the transom is too small for the off-the-shelf glass suction handle.
However, Seasucker makes marine suction cups which have stronger suction and are designed for marine use as well as being available in individual units. They have been used for an outboard mount on a Sup as you can see in the video below.
There’s also a Weta owner who has modified one of these canoe outboard mounts to clamp across the cockpit side at the stern so that the outboard is mounted at the side.