If you have a Druid take Wolf Domain.
Granted Powers:
Improved Trip: You gain Improved Trip as a bonus feat.
And use.
Domain Strike: When you gain this feat, choose one domain-granted power that you can use to affect no more than one opponent. If you make a successful unarmed strike against an opponent, in addition to dealing your unarmed strike damage, you can use a swift action to deliver the effects of the chosen granted power to that opponent. Doing so provokes no attacks of opportunity.
Does this allow a free trip if you attack with Unarmed?
