Sure you can rethread it. Something like this - http://www.permatex.com/products/Automotive/thread_compounds/a_thread_sealants/auto_Permatex_Thread_Sealant_with_PTFE.htm - should hold it for a while too. If it holds just keep topsiding your oil changes. JB Welding it would obviously hold but would be permanent. Changing that oil pan is a pretty big job. You might just want to become a devout topsider.