For me, the passive vs. active debate comes down to a matter of pure pragmatism. I don't want to roll 40 Perception checks if there are 40 combatants on the field, so I just rule that everyone is effectively taking 10 on their rolls which produces a completely average result for each creature; no really high rolls and no really low rolls. This also has the added advantage that I don't have to keep track of which individual opponents actually made their rolls and which ones failed. Tracking is instead by creature type, since all creatures of the same basic type have the same passive Perception score (e.g. all of the Kobold Skirmishers succeed, but all of the Kobold Minions fail).
This arguably has the downside of making things easier or more predictable for the rogue, but I'm willing to sacrifice predictability for the sake of keeping the game from grinding to a screeching halt. If there are just a few opponents involved, I'll go ahead and make one roll for each to keep the rogue from getting too complacent.
Sure, you could do that.
Me, I do it another way.
First, since a room full of kobolds would all have pretty much the samme passive perception value (since they are all similar kobolds), taking 10 (using passive perception) pretty much means every kolbold sees him (bad rogue stealth roll) or no kobold sees him (average or good rogue stealth roll). There is very little possibility that a few kobolds happen to be looking the right way at the right time and spot him (which is what a good perception roll would represent if I did take the time to roll each one).
Of course, the target of the attack needs an immediate perception check to know if combat advantage is granted. But the other 39 kobolds don't need any check at all. I see no benefit, now, on the rogue's turn, to knowing which of the kobolds can see him and which cannot.
Most actions the rogue might do will break his stealth anyway. So, one kobold needs to see him (or fail to see him), the rogue takes his action and consequently becomes unstealthed.
One stealth roll, one perception roll. Done.
But, assuming the rogue's action doesn't blow his stealth, I have him write his stealth roll on the battlemat near his figure.
On my turn, when I'm moving all those kobolds, I will look at the tactical situation.
Some kobolds will naturally go after the wizard, or the fighter, or whoever, because that's the PC threatening them. Essentially, I decide it like the rogue has no cover/concealment/stealth at all - which kobolds would attack the rogue if they knew he was there, and which kobolds would not attack him even if they can plainly see him.
I move all the kobolds who wouldn't attack the rogue without rolling their perception checks. Who cares if they see him or not since they aren't going to attack him either way?
For the remaining kobolds who would attack the rogue, I roll their perceptions before they act. One perception roll, then move the kobold accordingly (attack the rogue if he saw him, or go look for the rogue if he didn't, or ignore the rogue and attack someone else in some cases. Next kobold. One perception roll, then move the kobold accordingly. Etc.
This works easiest for me. No blanket "everyone fails" or "everyone succeeds" based on passive perception. No rolling for 40 kobolds. No remembering perception rolls made 5 minutes ago during the rogue's turn when it's finally my turn to move the kobolds.
Piece of cake.