done a lot of stuff, but not that one. Should be possible though.
What I normally do in situations like that, is tack the bits together, making sure everything lines up nicely. then grind one side down to the middle of the fin, tapering out to about 2 to 3cm. Glass that, turn over and do the other side.

Manuel7 said..
Im assuming you'll have a foil problem. The fin is profiled to be at an angle. So if you straighten it out the profile will be at 45 degrees.

Woops, I misread this as wave fin, not weed fin!

Yes cut off and rebox to the angle you want.
And Manuel, a lot of weedies are just upright fins reboxed, they suffer from being too thin, making them upright will just bring them back to their designed foil. If they were designed as weedies from scratch, then yes they will have a greater thickness to chord ratio, than designed by about 20%. Probably no big deal, they may be a tad slower but will work better in lighter winds, and you can get away with using a slightly smaller fin