I just did nearly the same thing last week. I used 2 scraps of ply epoxied together to give a thickness almost as tall as the T nut. Instead of one piece as long as the brace, I used a 1"x 1.5" block for each T nut and one in the middle just as a filler behind the brace to keep it from flexing. I haven't mounted it all in the boat yet.... so no results, but I'm thinking it'll work!.

: Hello All,

: Here is an attempt at foot brace mounting without through-holes. It is based
: on a low profile idea the Lee mentioned in a previous post on mounting
: braces as close to the hull as possible (for those with large feet).
: Although there was plenty of room for us to mount the braces with thicker
: blocks to hold the t-nuts, we had scrap 4mm Okume and no good scrap for
: mounting blocks. All of the hardware is stainless steel and the rails
: (Keepers) are plastic.

: The mounts are as long as the Keepers rails and were prepared by drilling a
: 3/8" hole for each t-nut body, four 1/16" holes for each t-nut's
: tabs, and a 3/4" counter-sink through one layer of the 3-layer Okume
: for each t-nut. The front of the mount was sealed and glassed with one
: layer of 6oz glass (at 0,90) and reinforced around the the t-nuts with two
: more layers of 6oz glass (at 30,120 and -30,60). Then I redrilled the five
: holes through the glass. Then I saturated all holes with epoxy, seated the
: t-nuts in place, and sealed the back of the mount. I plan to mark where
: they go in the cockpit and then glue them in with thickened epoxy.

: So, any comments, suggestions, warnings? Do you think they will be strong
: enough, etc.?

: Thanks,

: Tim.