I did the same as Paul and Sean, but just on half the kayak. The attached photo doesn't show the strip, but does show why.

I did the front half the usual way with tape inside and outside. Because the back half of the deck is so flat and meets the hull at almost 90 degrees, I thought there would be problems with trying to get the tape to fit into the angle. So I thought it was a good time to try a type of sheerclamp.

After the inside of the hull was glassed, I glued on a strip about 10mm square. Trimming it to the correct angle to match the hull was very easy.

As the kayak is a racing K1 (but with enough stability to stay upright), I just glued the deck on with thickened epoxy and glassed the outside of the join. Since K1s are treated with a lot more care than most sea kayaks, I thought that would be strong enough.

That method worked well, with no need to notch forms.