5th to the LE will relaunch both on snow and water, but if your stationary in a snowboard your looking at a little more wear to the kite as it skids across the ground more than the latest gen of easy relaunch 4 liners. You can avoid this by stepping out of the board and walking or skating on skis to keep the kite in one spot while you reposition during relaunch. Sometimes a necessity in real light conditions, and It still skids sometimes as snow/ice can be slippery! Thats just the downside of using tube kites on land. The 5th to the TE might save you some wear and tear on land, but you lose the 5th as a safety and you have to be careful it doesn't pose a hazard to your existing safety.
Have used a standard 5th to the LE on many C kites and they relaunched great on snow. Caution attaching a 5th to your kite if its not built for it. The attachment point should be pretty sturdy or you can damage your kite if it ever takes a sudden load.
Some of the newer 4 liners with wider wing tips are great as you can reverse relaunch em with just the rear lines. Basically doing exactly what your talking about with a 5th to the tail end or the struts. I routinely pop my current kites up backwards and spin em in really really light conditions. At this point I'm trying to dial in any technique I can that will decrease the wear from scraping across rough ice and snow. My latest kites are light years better at low wear and tear relaunching than my older ones. Something to keep in mind when buying your next kite.