I'm siding with the fact that Lelouch doesn't want a line of slaves waiting to do his bidding.

As for the eye contact thing, it's not like he has to say his command before they turn away. Once he's got them in eye contact, all Lelouch has to do is fire his Geass, and he's got them. He's done that multiple times, and with his more detailed commands, like the sniper that was to take out the Vincent not too long ago, the Geassed stand there and listen to him until he's finished giving the order. Other times though, he uses it quickly as he speaks to make it go undetected.

I believe he might have issued an order similar to the "do as I say" one we're discussing. If you remember back to the butler fellow who made Lelouch his mask, he brought the completed mask for Lelouch to inspect, and afterwards, Lelouch comments "now all there is to do is destroy the evidence.", after which the butler promptly carries out. If we extrapolate that conversation, I think that it's very likely Lelouch gave more than one specific order to that guy. It may not have been "do as I say", perhaps more specific, like "help me make a mask", but for our purposes, it shows it's entirely possible for Lelouch to issue an order that leads to them taking more orders.

After all, his Geass is one that commands absolute obedience, regardless of the scenario.