I have a bit of an idea,

Instead of filling up the unused holes to suit the 4-hole S203 wing brackets - and thus making the whole boot somewhat useless when I decide to get rid of the wing and boot, what material would I need to possibly fab up and underlying support piece, that will hide the hole and cover the existing S203 ends?

I would want it to be around 5mm thick, and have the same shape as the bottom of the S203 bracket but have enough width to extend along to the other end - in turn covering up the holes along the way.

Heres a pic of how it will look like now:





and a pic I found on the net that gave me the idea for my setup: