In researching my comment above, I came across this synopsis of Action Comics #366:

“The substitutes are really five Justice Leaguers in disguise, who were filling in for him while the Kandorians chose a successor for Superman.”

… which answers your question about how long the Leaguers were going to keep this up…. but it opens up other questions like, uh, if you can release ONE of the Kandorians, why not let them ALL out?!

Ok, I’m all geeked out.

I just finished JLA Archives Vol 8 last night, and it includes a story where all of the team members go out and dress as Green Arrow (Issue #61 – “Operation: Jail the Justice League”). Well, except for Wonder Woman, although we do get a humorous panel of her looking in the mirror and deciding that it won’t work. (Perhaps someone more technoligically advanced could send you a scan?). Both the JLA issue and the Action Comics issue were published in 1968.

It is amusing to think that Aquaman, Batman, the Flash, Green Lantern, and J’onn J’onzz all have a Superman costume AND a Green Arrow costume in their closets. “Hm, which superhero should I be today?” (Ok, fine, not J’onn. He can be whoever he wants. Even Wonder Woman.)

One last note: in the JLA issue, the Atom’s Green Arrow costume was made of that White Dwarf stuff. It must have been the second most common mineral in DC’s Silver Age, after Kryptonite. Sheesh.