Maybe smear on some Aura of Smooth?

(Awesome idea, the infiltration, wish I was doing it. :p )

Grab a few Andalite Agents, get them to 'acquire' a Sue/Stu. Though, the psychological repercussions might not be fun, and if one of them got stuck... anyway, I know I've read about at least one Andalite Agent.

Also, someone from the Young Wizards continuum might be able to put together a mochteroof - kind of a solid disguise that one "wears", if you're not familiar with the term. Might something like that work?

Aside from the DORKS, they can use more mundane methods. Dye their hair some outrageous color. Get colored contacts to change their eye color. Put on copious amounts of make-up and outlandish, impractical clothes. Make up a long, involved, fruity name, and be sure to tell everyone. Most of all, act like the 'Sue type they're emulating. Mostly, it would come down to acting. Even if they went without disguises, they could pull off Goth!Sue (from all the black) or Average!Sue (when they look normal but are still speshul). As July said, it's all in the attitude.

Of course, it's much more fun to dress up.

That it's not the appearance that makes a Sue.

But the actions.

So arrogance and confidence and probably a touch of makeup would work for a disguise.

And besides, I've found that so long as you /look/ like you know what you're doing and where you're going, people are less likely to interfere. That'd probably hold the same for these infiltrators. *grin*

My suggestion would be Agents from the HP Continuum, with Polyjuice Potion, Agents who are capable of turning into things anyway (I.e.: Paddebrains)or those capable of altering the perception of others through illusions and the like.

Assuming Sues aren't resistant to having their minds controlled (Doubtful, none of them seem to have a mind anyway), then Agents with psychic powers will be able to attend as well, by using their powers to change how others percieve them. Downer to this is that some Psychic Sues may notice, but Agent Lunac has several devices from the Pokemon World which block psychic powers.
And lastly, but not least, you can always have the Agents who don't fit into any of the above categories to simply be invisible.

My first question is...what's the EPC?
And I agree with Cassie. Send in ex Sues/Stus. Or maybe send in the non-human Agents, if you would like to be more general.

I assume they'd still be able to turn on their repressed qualities if necessary. I think I read that one Agent keeps having to apologise for causing urple descriptions or something.