*Disclaimer* Although I have owned 5 mopeds
(NC-50 Express 1978)
(Tomos Targa 2000)
(2 QT-50's 1982)
(Tomos Bullet, 1992)
the majority of my knowledge comes from reading the great posts. I'll have a lot more hands on experience soon--with the garage/shop.
That said, it would seem like you could put in a new plug (I'm assuming that's all you need to get done, right??) and somehow use JB-Weld or some other Epoxy/Metal type substance to use as a seal/gasket.....essentially making your plug and head a single unit....
I would be worried about getting that gunk into the engine though. i try to think: "What would the guys on Junkyard Wars do to fix this...?"
If you're going to be replacing it anyway, there must be some way to get a plug in there and secure/seal it without losing all the compression---
As per the disclaimer, this might be an absolutely stupid idea---You're the one who asked about "bodging" it.
McGuyver would get that moped going with one trip to the hardware store.
Fred's even better than Mcguyver, so there has to be a temporary fix.... until you get the upgrade.