Here's my own stab at solving this.
Edit: Because of several issues with Skill Challenges in general and mine in particular, I am reposting my simpler Endurance check based solution from below here too - I have concluded it is the mechanism I most want feedback on!
Pressing on - Forced March Endurance Skill Checks
Each hour, every character in the party must make a
Moderate DC* Endurance skill check.
*) A Moderate DC is 9 + two thirds the level of the party or terrain (rounded down). An Easy DC is five lower, a Hard DC is five higher.
Apply a special Hours Passed penalty: -1 per hour for walking (above the first ten each day); -2 per hour for running. This penalty applies to all skill checks made while pressing on, not just Endurance (see below). An Extended Rest reduces this penalty by 10 (to a minimum of zero). If the Hours Passed penalty is more than -10 when you take an Extended Rest, that Extended Rest provide no other benefit other than reducing the Hours Passed penalty.
Failure means you lose a healing surge (but see below).
Success means you do not lose a healing surge, and you may assist one of your failing companions.
If you succeed on the Endurance skill check, you may assist a failing party member in one of the following ways:
Heal: Your Heal check can stand in for another character's Endurance check. (That is, make a
Moderate DC Heal check. Success means the assisted character succeeds on his Endurance skill check after all.)
Nature (or Dungeoneering if below ground): Your Nature check can turn that character's Endurance check into an
Easy DC one. (That is, make a
Moderate DC Nature check. Success means the assisted character get +5 to his Endurance result, and might make the check after all.)
Perception: Your Perception check can "aid another". (That is, make a
Easy DC Perception check. Success means the assisted character get +2 to his Endurance result, and might make the check after all.)
Endurance: You may take part of the assisted character's burden upon yourself (carrying that character for short stretches, helping him climb obstacles, and the like). Make a
Moderate DC Endurance check. Success means you spend the healing surge in place of the assisted character.
Players are free to focus their assistance where it is best needed - if a companion fails his Endurance check by more than 7, for example, Nature/Perception can't do anything for that character. You decide which character to assist only after everybody have made their main Endurance checks, but before anyone roll their assisting skill check.
The only restriction is that two or more characters can't use the same skill to assist any given character. (You can get Heal assistance from one companion and Endurance assistance from another; but you can't get Heal assistance from both).
And to clarify...:
* A character whose Endurance check is turned from failure to success does not get to assist anyone that hour.
* If noone fails their Endurance check, no assistance is needed. If everyone fails their Endurance check, no assistance is possible. Simply move on to the next hour's checks (unless the party have had it, and decides to rest).
If you miss the way the more elaborate Skill Challenge (see below) additionally tells you when you stumble upon a monster and when you find shelter; an easy suggestion is to use the times the characters roll '1' and '20' on their main Endurance tests (not any voluntary assisting skill checks).
Whenever you roll a natural one; roll again. If you fail your Endurance check (unassisted) on this second roll that equals "combat encounter at level + 1".
Whenever you roll a natural twenty; roll again. If you make your Endurance check (unassisted) on this second roll that equals "secluded shelter; reduce the Hours Passed penalty by 2".
Zapp
PS. If you feel there's an awful lot of rolling, feel free to say rolls are made only every two or three or five hours. In that case, however, you should probably consider making each failed Endurance test lose two Healing Surges (or, for the longer periods, make
everybody lose a Surge each).