Nice effort, cspaur!
You've staunched the flow to where the drip is more of an annoyance, than a catastrophic threat. Keeping an eye on the oil level, and a drip pan in the garage can keep you on the road.
(I assume you used a new crush washer and the leak is still present.)
If the case is cracked, chances are it cracked when the original plug was stripped, not upon insertion of the oversize plug, IMHO, because the slightly oversize diameter and self-tapping tapered threads aren't likely to split the hole. Then again, a pre-existing casting flaw may be there.
Next step? Might be able to drill-and-tap to a slightly larger size, although there's not much "meat" around the hole. Alternatively, cleaning up the area and J-B Weld (may need some release agent on the plug) could save the day.
Inserts (e.g., Timeserts or Helicoil, etc.) offer a permanent repair.
A rider I know cracked his case (Generation 2) and had it welded successfully; I'd imagine a shop that knows what it's doing could fix your bike similarly.
Best of luck, whatever additional solution you may seek; please let us know how it goes.