Wow, talk about a solution in search of a problem and to lighten your wallet considerably...The one you linked would be fairly easy to make as mentioned.
If you wanted to buy some, these guys have a cool design and make it for Frontiers but it is priced accordingly.
It appears that when using that type of item it's holding the gate almost in position to remove the gate which is why mine has 2 thick zip ties so it never can pop out.
Why not just use a bed extender? It fits around the tire and retains the ramps from falling out and straps to the latches to keep it and the gate from moving over bumps as well.