Well, the magnetic drain plug will likely help and maybe even the magnet on the oil filter mod
that The Modfather did.
Of course, any case metal will be aluminum/magnesium and won't be attracted to a magnet. Hopefully the oil running out kept most of it out of the case.
So, here is my idea for a long-term fix (I'm hoping that the thread sealant will get you through the rest of the season). This also assumes that you threaded the hole all the way through (or can) but it requires no welding and could be done at home:
a. Pull the case apart (again...arrrrgh).
b. Clean the snot out of the hole with solvent to make sure it is 100% clean and dry. This will undoubtedly require cleaning the whole case half but it allows you to verify that there are no metal shavings left in the case.
c. Get a flange bolt of the proper size that will thread in to the hole. This bolt will be placed into the hole from the inside
and should be as long as possible but not so long that it interferes with the cover bolt coming from the other side (outside).
d. Thread the bolt into the hole from the inside and verify that the bolt head does not interfere with anything in the engine...you might have tons of room or it might be really tight...or just flat impossible. If the inner face where the bolt goes in happens to be flat where the head of the bolt actually snugs up all the way around (yeah, like that'll happen), you could add a copper washer that will fit on this inner bolt to help seal things but be sure to check clearance with the internal workings with the washer on it.
e. If the bolt does not interfere with anything inside the case, mix up some epoxy (like JB Weld), cover the threads of the bolt with it, and then screw it in and snug it up. Between the bolt and the epoxy, you should have a seal that will last forever.
If you find that the bolt head does interfere with something or, you just don't want to take the chance, you could cut the head off of the bolt and, using a hack saw, die grinder, etc. cut a slot in the end of it to act as a screwdriver slot. You could then do the epoxy thing but screw the bolt/plug in with the screw driver until it is flush on the inside.
Either way (full bolt or just threaded part with screw driver slot), I'd do a dry fit on that to make sure the cover bolt still goes in far enough to snug down the cover before doing the epoxy thing.