'Play the Game' featured Andy Gibb singing backing vocals alongside the founding members. Frederick was quite impressed with the result, so they may have ended up on the final cut, unless of course lyrics changed or something like that.
Mike Stone on Good Old Fashioned Loverboy. The lady voice on Leaving Home Ain't Easy is Brian with a pitch shifter/tape speed change as far as I can tell.
Oh okay, sorry, DLYH was mentioned before :blush:
Then, optionally: the dialogue snippets from 'Flash Gordon' and 'Highlander', and since there's a mention of C-lebrity I throw in the Barcelona album. :D