Guys, don't choose the more convenient interpretation of my quote just because you don't remember Lelouch being such an asshole. Lelouch wasn't talking about filling the urgent need for somebody to occupy Ougi's 'position', he was completely
discarding him as even a pawn on an individual level. Here is the full quote again for your benefit:
"Ougi? It's me."
"Zero? Thank goodness..."
"Minami? What happened to Ougi?" <-- indeed, I got the name wrong
"He was shot. He has lost consciousness and is currently undergoing treatment. In addition, the culprit is still..."
"I understand. You'll suffice then." <-- Minami is already assigned as a replacement for Ougi's 'duties'.
"Can you go find what the girl in the wheelchair is doing?"
"Well, before that, Ougi is..."
"I'll think of a replacement for him later! Right now, the girl in the wheelchair comes first!"
"Replacement...?"
As you can see, the 'disposable pawn' aspect comes from Lelouch's complete disinterest in ensuring his pawn will even stay alive, not a (reasonable) willingness to assign a substitute when said pawn is unable to fulfill its duties (because, in fact, Lelouch
wasn't even willing to seriously do that at the moment).