If you'd like your character to help Vorrin repair the chasm, make a Wisdom check at DC 10 to Aid Another. He has Autohypnosis trained, so I've decided (via PMs with Baronsquee) that Autohypnosis should be applicable to shaping Limbo. It seems thematic to me. If you'd like to do any other form of chaos-shaping, it'll be a Wisdom check at DC 15 to temporarily control a sphere with a radius of up to 10 feet. Characters with a Wisdom score greater than 20 can permanently stabilize an area.
We can use the rules in Manual of the Planes if you like, but they're basically the same as the above, just needlessly complicated and a bit less generous.
For future uses of Aid Another, let's also use the semi-optional Expert Assistance rule:
[sblock=Expert Assistance]
If you have 5 or more ranks in a skill you’re using to aid another, you can grant a higher bonus. For every 10 points your check result exceeds 10, the circumstance bonus increases by 1. To determine the circumstance bonus quickly, simply divide the helper’s check result by 10, round down, and add 1.
At the DM’s option, this rule can also be extended to using the aid another action in combat to improve an ally’s attack roll or AC. Any character who has a base attack bonus of +5 or higher can grant a greater bonus on an ally’s attack roll or AC as described above.[/sblock]