I am used to fixing them with the "nut" exposed but this one is buried in.

Even as a temporary repair, could I just pour superglue or epoxy into the hole?

Any ideas welcome.

Easiest way is to drill a hole across the bolt hole and insert one of these .http://www.sunshinecoastsailboards.com.au/shop/spare-parts-repair/crossnut-detail

youll find the thread is tapped into the glass ,and that's what will have stripped. need to drill out the bolt hole so the bolt goes in easy , drill a hole across the bolt hole about 15-20 mm down , the hole needs to be the same as the outside of the insert , then just push it in , they have a slot on the end so you can spin it in the hole to line the thread up.

pulled me out of the **** many times , I had a bolt snap of in the thread once , inside the fin could not grab it ...tried everything I could to get it out , easy outs ect .... Ended up having to cut the broken bolt out with a grinder , made a big mess of the area around the fin where the thread is . Laminated the fin back up with epoxy and carbon , drilled out a new hole and inserted one of the inserts , still going 3 years later.

Like this , the carbon one is the one I had to dig the busted thread out of , the other ones just stripped out.

It's a Vector Canefire and there's no nut in it. the treating is in the fin head itself. I will have to do the very same repair on a Canefire 40cm. insert a bolt and mark the direction further down the head. Measure the vertical position of the nut on another tuttle head and drill a hole on the line you just made. Drill out the old threats so the bolt goes easily to the new nut position. insert barrel nuts and a bolt and glue the nuts in the right position. voila!