Erch. That is tough.
Um. Well, I assume that, in order to be the kid's godfather, you have to be officially Catholic, and to be officially Catholic, you have to be officially reinstated, or whatever. Anyway, first thing I'd do is talk to the kid's parents, and explain to them your situation (I'm assuming that this little discussion isn't out of the question for whatever reason....) If you have to, you can tell the kid that you are honored, and WANT to be his godfather, but because you're not a member of the catholic church, you CAN'T (not that you WONT, that you CANT.)
Um.
I dunno. That's just what pops into my head. Might not work, and it's been a long time since I tried reasoning with an 8 year old, and I have no idea how rational the kid is. Pretty reasonable, I expect, given that you like him.
On the other hand, I mean, like the others have said, you could just "suck it up" and take the course. I mean, it's not like you're being converted in actuality, just in the eyes of the Church, which is not necessarily the same thing.
I mean, heck.... I have Jewish relatives, and while I'm not Jewish, my religion and Judaism are hardly mutually exclusive, so when I'm visiting them, I'm perfectly happy to not only adhere to all the rules about kosher and all that, but to even participate in their... I'm not really sure what to call it. Not 'rituals,' that sounds too cultish. But you know what I mean. I'm not Jewish, but I don't have a problem with participating in Jewish stuff. NOt because I think its necessarily right, but because I don't think its wrong.
Your call, of course. I mean, it depends on what exactly this course consists of. If you have to stand up and swear your soul to the Catholic Church, that's different than sitting in a pew through a few extra masses dedicated to renewing your official membership.