Try the puddy stuff like "Quick Steel" or similar. Can be found near plumbing department in hardware store. I carry some when I ride. Lots of riders of all makes and models have cracked their side covers or punched a hole. I'm actually using some right now to help seal the left side cover gasket near the starter. I let it sit overnight after I applied it. It's been on since last October and no leak what-so-ever. And it's hard as a rock. Of course I'm not sure how easy it will be to take off when I need to take the side cover off. I'll probably have to re-apply it as my side cover is ok, but the engine case has a chip out of the surface area where the side cover gasket would seal up to it. Hey, it worked once it should work again.
I can't remember the exact brand, but it looks just like this when open up.
You can also get some metal JB Weld Epoxy. I haven't used this on the side cover, but have seen it applied. Not sure how long it lasts. I have used it to repair plastic gas cans with some success. Just doesn't work on a smooth surface very well, so you'll have to rough up the area pretty good unless the crack is big enough to hold it.
Hope this makes sense.
Of course I would consider these as temporary fix's.