We have Oramus' and Ebon Dragon's excellencies as well. And the excellency isn't the only charm he has; his leadership and group-buff charms are the ones I'm touting and so far no other Yozi has anything comparable to them.
Getting an Excellency that is sufficiently different from those two will be rather helpful as it increases the range of actions we can boost with an Excellency. It would be very wasteful to get a Yozi whose Excellency we can't actually use, especially this early on.
And as other have said, learning how to acquire new names is a solution.
And we can purchase or create a charm to make 'Zero' our identity. This isn't hard.
Any such Charm would probably still violate the Excellency's conditions unless it truly twisted Lelouch into Zero. For example, Name Shrouded Under Veils creates a false name that only appears true for the purpose of Charms and techniques that determine whether or something is true or not, but it is in reality still a deception so wouldn't work with this Excellency. Remember that Masque of Hollow Faces and everything that follows it is build on masks - it's fake, not real. The Ebon Dragon is similarly about deception, except when he turns into your shadow mirror, but then you get that person's Charms rather than keeping your own for the duration of the change.
To make a Charm that would truly change Lelouch's Name into Zero for the purposes of this Excellency would probably require a Charm that requires a shitload of motes and willpower to activate or would have to twist him in a much more permanent fashion. Anything in which Lelouch would know he is hiding his true identity just wouldn't work. A real change of identity would be required.
What value would Malfeas offer us? His excellency is broad, true, but that's just one charm. All his other ones relate to personal combat or terrorizing people into obeying. I think it would be a waste to unlock a Yozi from whom only a few charms truly offer benefit, especially since we already have a Slayer to do the frontline fighting.
Knightmare combat is a thing. A major thing in Code Geass, really. Lelouch already has the specialty maxed out, and we definitely want to max out Drive. Malfeas's Charms could certainly be used to help with Knightmare combat, even if it requires making new ones using the Innovation keyword to make new Charms for that. Getting Nightmare Fugue Vigilance to remove the need to sleep would also be useful, as it'd give Lelouch extra time to do stuff. (Oramus definitely isn't a 'no sleep' kind of guy, so a custom Charm there wouldn't make sense) That Charm might also be a good basis for mixing with Ululating Nightmare Wings or something coming after that to make something Heretical. (some kind of waking nightmare Charm that makes it almost impossible for someone to sleep?) Other Heretical Charms could also be made.
Also, Akito can't be around all the time, or there's a chance he could be overwhelmed if fighting against multiple opponents. In such cases we need someone else in the Coven who can take up the slack. Lelouch is unfortunately the best candidate for that, I think.