Man, I just read the whole thing, I don't know what is wrong with you Caliban, but it seems to me you are in a bad mood. That's just my opinion, and I don't want you to take it the wrong way.(then again, how couldn't you take that the wrong way... hmm... nevermind) Anyway to the topic at hand. Rules are made up to be bent, adjusted, manipulated, or otherwise followed to the tee. We use rules to get more fun out of the game. If you can do what AirElemental said, without argueing about the alignment of the character. Lets take for an example, a Lawful Good character summoning the Archon. He tells the archon that this bad guy, who happens to have a sword of soul stealing, and that without it the whole city dies, then I think the archon would go ahead and try to aquire the sword. Sure it would take a lot, or just wait till the guy was asleep, which is the best way I so far seen. Anyway, it would work. It can work, the rules back it up, it is clever, something that should be rewarded, not demeaned. So you use the archon for the personal gain. It could say no, but in reality it shouldn't, there doens't seem to be any reason why it can. It is under your power, you summoned it, not someone else. It isn't in nature, it is under your power. So, with that respect you should be able to summon anything you want. But where this should be prevented is at the gaming table. A house rule, or DM judgement should say that you can only summon things that are either close to your alignment, such as CG summoning something that is Good or Chaotic, never evil or lawful. Or CN, only things that are Chaotic, and never lawful. If you summon something that is stupid, too bad.
So, lets look at the idea again, using the 4th level spell to use a 7th level spell... sort of, but not quite, you aren't placing yourself in danger, something else, and it won't work unless you use a lot of preparation and planning. You have to scry the person, find out exactly where he is, use major image, after you cast the summoning, to tell where the guy is, while telling the creature in exact words what you want it to do, which we have already found does not require you to be able to speak celestial(it has tongues). Then to ensure it works, casting haste, improv invisibility, maybe stoneskin. It might have one round to do it... heh. But it can be done, it is within the rules. If I presented this to my DM explained it carefully, showed him that it can be done, and it's entirely limited scope, then he should say yes. If he doesn't, well, then I should think about playing with a DM who plays by the rules, not on some whim. I agree that the DM has every right to say no, but why should he. It is within the scope of the game's rules. I as a DM would allow it, but more often than not my NPC's usually spot the Scrying, the will know something is up. But in very specific, needful areas, where it might be the last resort to get an item from an escaping enemy. Yes, it more than likely would work. AND it is a good idea, the using of the Archon, not the evil guy trying to use it.