That is definitely...unexpected. Not the end of the world, but unexpected.
I'm in the "wait and see" camp as far as whether this is a good idea or not, since execution is everything and surely we won't know the official explanation until episodes 3 or 4, but in the meanwhile...I think there are a couple of possible answers to the questions raised by AmuroNT1 above.
1) We don't know about the specific limits of the Geass abilities used by Charles, especially since his power is distinctly different from Lelouch's, but the existence of several other multi-use Geass abilities means we don't have any solid way to rule it out either. Which also allows Sunrise planners and the creators of Akito the Exiled to potentially make a decision in whatever direction suits their purposes. You can blame the lack of sufficient explanations for most of these infamous magic eyes. That much would add new information to the equation but it wouldn't break anything.
2) Based on previous comments made by director Kazuki Akane, specifically in a two-part interview on the official website, I think this might turn out to be more about Suzaku than about Lelouch. Maybe it's a way for Charles to further test his loyalty? In that sense, the one being mocked would be Suzaku, not Lelouch. To quote said interview:
-The appearance of C.C. and Suzaku has been announced for Chapter 2.
I'm interested in the character of Suzaku in [Lelouch of the Rebellion]. Though he’s the son of the Japanese Prime minister, he became a soldier of the Holy Britannian Empire which conquered his homeland. He always has to face that contradiction, and furthermore learns that his best friend Lelouch is Zero. I think that that pain is on a level that others can’t understand at all. That's why I will make the anguish-filled Suzaku…Ah, if I say anymore, I’ll be giving away spoilers. (Laugh)
Translation by Eternal_Dreamer. The Japanese source is available here (please click on the second part):
http://www.geass.jp/akito/interview.html
There's also the possibility that the underlying goal of the visit is secret (in other words, not just "helping Euro Britannia defeat the E.U." or something similar) and not the kind of affair that Charles wants someone like Schneizel to be too involved with, even if he doesn't mind letting him get all the military or political glory later.
However, I won't dismiss that it could turn out to be another person entirely. After all, this is Sunrise. But just as well, compared to some of the crazier things that R2 pulled off...the other alternative doesn't seem impossible either.