Hick Trick
Drain all of the oil out of the pan, really good.
Spray the crack with brake cleaner to clean it really good.
I'm assuming this is a hairline crack and not a chunk missing out of the pan?
Once it dries (an there isn't oil continuing to seep out of the crack) get some "JB weld" or "PC-7" from you local hardware store, mix it up as per the instructions and spread it over and around the crack, press it in there really good. Let it cure over night or whatever the instructions tell you. Once it is cured, fill the crankcase with oil and start her up.
It should last you a little while, sometimes even permanently. But if not, you'll have to re-weld or reaplce the pan. The pan is cast aluminum. So make sure if you re-weld it that you use a MIG welder with an aluminum spool.