A little impatient? 8:47 reply, then a 9:10 "I give up". Come on, I stepped out for a coffee break.
I am curious now if you actually had another user though. You say the only entry in the groups file was for root? If you had another user, then you should have seen an entry for "users" or a group matching the user accounts name as well.
Anyway, you would've needed to get the numeric value of the wheel group and then modified the entry for the user in the passwd file. But I would have to boot up my linux box to recall which field is the group. I think it's the 3rd field, but I may be wrong.
There were other ways as well, for instance, you could have chrooted to your / partition, then added a user, with wheel as the group. That's one of the fun parts of linux, is finding all the ways that you can do the same thing.
Good luck on the rebuild, never hurts if you can spare the time and won't loose data.