<< Interesting. I always thought it wasn't another word at all, just a repetition of the final syllable for rhythm-maintaining purposes.

"know, -ow,-ow,-ow", pronounced "oh, oh, oh." >>

Very possible. I presumed it was "whoa," since in the next line they sing "Heaven holds a place for those who pray, hey, hey, hey."

I guess since it's "hey" I thought "whoa" was the other. You're right, though, whichever it is, it's meant just to be a rhyming extension and nothing more.