Hmmm.... my DM has run a few skill challenges with secondary goals. He says they are stolen from Pcat's campaign.
No kidding? I'm flattered.
If I were going to do this, I'd set it up something like this. I'm just pulling this out of my butt; it needs refining. Fast version:
Part 1 - you camouflage the camp. At the end of Part 1, a quick combat occurs.
Part 2 - you reinforce the camp tactically. Succeed and part 3 gets way easier.
Part 3 - the ritual casters try to finish the ritual, while everyone else works to keep the bad guys away from the casters.
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Hold The Line
You have sixteen hours to learn and cast the ritual, but your enemies are closing in. Can you do so in time?
Part One: Enemy Intelligence
Keep the camp hidden, one way or another. It's only a 6/3 challenge, but the DCs are set relatively high. Success means a +1 bonus on all skill checks in parts 2 and 3. Failure means a -1 penalty on all checks, as the enemy has seen you and maneuvered its forces to more effectively harass you.
Primary skills: Nature and Stealth (to camouflage the camp), perception (to spot enemy scouts in time to get people out of sight)
Secondary skills: Aid another can help another person's roll. Insight, figuring out which way the enemy will come, can also grant +2 but can only be used once.
Special: the ritual caster can contribute with one arcana or religion check, whichever is appropriate, as they prep their ritual.
After Part One is completed, a few enemy scouts stray close to the camp; if Part One was successful, they don't see it and can be ambushed by the PCs. If Part One was a failure, they turn and flee to report back. they can still be attacked, but they start at long range and would rather flee than engage.
Part Two: Reinforce the Camp
This is a 8/3 challenge, but the DCs are a little lower. The goal is to dig ditches, set up traps, and so forth to reinforce the campsite. Success means an additional +1 on checks in part 3, as well as the ability to impose a free one-round Slow effect on any two enemies per round in the Part 3 fighting. That simulates your traps and defenses slowing the enemy down. Failure means you've left your site exposed, and two enemies per round attacking you in Part 3 gain +2 to their speed. [Note: that's just arbitrary, really - I want it to feel like you're being swarmed by the bad guys if you screw up part 2.]
Primary abilities: Athletics, Endurance, Insight, Intimidation, Nature, History (you know about good historical battle tactics), Thievery, Stealth (camouflaging pits), stuff like that.
Special: the ritual caster can contribute with one arcana or religion check, whichever is appropriate, as they prep their ritual.
Part two simulates the build up. Enemies start appearing and harassing you with long distance arrow fire while you're working, but staying far enough away that they are more a nuisance than anything else. Their presence is worse if Part 1 was failed.
Part Three: The Ritual
The ritual nears completion as the camp is swarmed. 6/3 challenge for the ritual casters only.
The ritual caster(s) make skill checks while everyone else keeps them safe. The camp is swarmed, mostly by minions, and everyone has to keep the enemy out of the area near the ritual casters. That means you run a combat (with the PCs gaining +2 to -2 to hit, depending on how Parts 1 and 2 went) with foes closing in on the camp site. At the same time, each round you have the ritual caster (s) make Endurance, arcana or religion checks each round to keep focused on what they're doing; they're also at +2 to -2, depending on how the previous challenges went. Each attack that hits them in a round penalizes their next skill check by 1 per successful attack. Any round a caster chooses not to make a skill check counts as a failure (they could spend an action point to get off an attack, though, so long as they spend a standard action casting.)
Success means that the other PCs kept the foe away long enough for the ritualists to finish the ritual. Failure means the ritual is ruined, probably because the camp site got overrun.
If you have NPC allies, feel free to let your ritual-casting players run them during the fight; that way they get to engage in combat too.
Thoughts, comments, improvements?