One of the Berserker feats from Frostburn gives you another +4 on tripping.
Wolf Berserker from Unapproachable East does that, but you'd have to start out as a barbarian member of a berserker lodge of Rasheman... It also acts as a prereq for Improved Trip, though. So you can take it without needing Int 13 or Expertise.
Damn, I got mixed up...
Barbarian would seem a little tricky, and after doing some looking myself, it looks like genuinely optimizing tripping will be hard, though I'll still take improved trip. The premise of the setting sun school is "strength is an illusion", yet their signature powers rely largely on strength
Fist of Dal Quor could add some damage via sudden strike and advances stunning fist attempts nicely (and you can blow PPs to increase the DC). It's actually a comparatively nice monk-like class. Unfortunately sudden strike can't do non-lethal damage. However, as long as you don't kill them no one says you can't injure them, right? If you use Martial Spirit stance you can heal them after downing them . Shape Soulmeld(Therapeutic Mantle) (along with Azure Talent to add some power points which you can blow on the stunning fist) can dramatically increase healing with Martial Spirit.
Actually, the VoN & VoPeace feats stipulate that you can never do anything but non-lethal damage, but can't sudden strike be made nonlethal with an unarmed strike? Sneak attack can be.
Also, I was looking at Nifft's very impressive collection of ToB homebrew, which includes a martial monk and the Sanguine Lotus/Crescent Moon schools (
http://www.enworld.org/forum/d-d-legacy-house-rules/187901-tob-bo9s-niffts-compendium.html). They seem well made to me, but I would appreciate second thoughts from anyone who has played with them. I figure there must be someone besides me who has run a ToB themed campaign and gone looking for more material.