You can certainly use a skeg that's held in place with straps of some sort. Its common practice in Greenland even today.

At the bottom is a link to some information on documented (old) Greenland skegs.

Here are a couple of images from the QajaqUSA galleries that show Greenland kayaks with strap-on skegs (and some detail about the straps):

http://www.qajaqusa.org/gallery/main.php?g2_itemId=29764
http://www.qajaqusa.org/gallery/main.php?g2_itemId=36209

I couldn't find any image that showed the strap arrangement deck-side, but usually there is some kind of tie in the middle of the straps on the deck pulling the two straps tight to keep the skeg in place. I have read that this type of skeg is considered permanent in Greenland, and the straps are often painted over when the skin coating is touched up.

I tried making my own version, but it wouldn't stay on the kayak. One might try to use some kind of rubber cord or rubber-coated cord/straps to help keep the skeg in place. The longer and more acute the angle of the two sides of the boat are, the easier it will be to keep the skeg in place.

The beauty of the strap-on skeg is that you can adjust its placement to change the effect it has on handling, without permanently modifying the hull.

: Figuring many will consider this sacrilege (sorry), but curious if anyone has
: attempted a temporary/removable skeg for the Guillemots?