This may sound awful, but I'm actually thinking of implementing them in the framework you're running (or the application "firewall"? Think a firewall/proxy that

This may sound awful, but I'm actually thinking of implementing them in the framework you're running (or the application "firewall"? Think a firewall/proxy that adds vendor prefixes based on your user agent. You write your CSS without them. Are there products that use this? How does it affect performance? I'm on an iPad right now so I don't really feel like Googling.