the section you are having trouble getting to is very easy to stitch if the adjacant wires are loose.
just use needlenose pliers to reach in the gap to thread the deck from underneath if the yak is right side up.
i/ve done this 100's of times on one of the s&g yaks i'm building on extremely awkward and completely unreachable areas from the inside.

loosen up the wires adjacent espec to the end as more flex and do above in the tricky area w/ the straight wire ends poking out of the gap.

have the 3-4" long precut wires handy. take the needlenose to an end of one wire and put a 270 bend in the last 1/4" , insert the wire just abt all the way in the fixed panel (not the new panel), the bent end pointing away from the gap and reaching in the gap with the needlenose or the wire is sort of prebent in a circle so will come back out the opening. then thread the next wire - no tightening till later

then just grab the last 1/4" of the wire(s) sticking out of the gaps and push it back thru the gap and 'feel and look and judge' and poke the end out of its hole in the next or deck panel. at 1st it'll take 8-10 secs - soon it'll be easy - you can judge distance, angle and feel the roughening next to the hole as well as see the shiny end of the wire thru the hole.after all done, carefully pull the wires semisnug as they're sort of kinked up from going in and out of the gap and it'll then be a dream.

after stitch up, glue betw the wires, then untwist and pull them out etc etc.

all you need is space for the needlenose to fit in.