Easy.
You set up an Ambush. In a forested area, for example. When you Hide, you don't take 10 on your check. You take 20. You have a good deal of time to prepare. Your fellow conspirators aid you ("aid another", +2 to the check). Scent won't work against the wind. ANd remember the Spot check penalty of -1 per 10 feet. (so -3 to check at 30 ft. vs 20+Hide+for aid, not so simple)
Then the first, immediate ambush is designed to only to take out a single character, or drop them so low they aren't inclined to do any real heroics. (Preferably the mage or a rogue)
After achieving this, the ambushers flee (earlier if they are obviously outgunned).
Of course the party then gives chase. Only certain characters are faster than others, and some are more eager than others for blood. Generally the clerics are very slow, and quickly left behind. They may not even bother following at all, assuming the battle to be won.
The fleeing ambushers, now lead those fast bloodthirsty few (often lightly armoured dex fighter types) following into a second, serious ambush, several rounds away from the original "ambush", and proceed to slaughter them. Discovering this ambush is much harder, as they are most likely moving as fast as they can to catch the fleer (counts at least as distracted -5, in my book. Should probably be as severe as -10). Thus, the well hidden will gain ranged sneak attack bonus (if rogues, with Rapid shot...), and anything else nasty you can think of. Notice that running causes them to lose Dex bonus to AC anyway...
Now the party is split, and probably lacking any real healing ability beyond a potion or two, at the area of critical focus.