Thinking about how the game works, I can't imagine that'd be possible... The UI doesn't log who completes the challenge, just that it has been completed. As far as I know, at any rate.
You can always just say to your guild to approach you for a reward after each challenge, assuming your guildies are trustworthy. And if they aren't trustworthy, why are they in your guild? :P
Yeah thats my backup plan. going to have them send me an in game mail when they complete a guild challenge and ill keep track of it and reward people weekly. I was just hoping there would be an addon to make it a lot easier on me