Instead of a post commit hook, what you want to do is listen for check in events.
- Client side - write a small utility that listens for checkin events. Effectively it's a small listener app and you set up TFS to send notifications to it using the bissubscribe tool. It's a little old, but this article should give you a starting point.
- Server side - write a custom event handler. The basic idea is shown in this blog post, just be aware that changes to your event handler will cause the TFS app pool to recycle.