Can NGINX do content based redirection?

I'd like to be able to us NGINX as the single point of entry and send the traffic off to different servers depending on the content of a SOAP/XML element, is that possible?

So the SOAP request might POST <colour> BLUE </colour> and it would reverse proxy to server 1 but if it was <colour> RED</colour> it would send it to server 2. I know you can do it with GET requests ($arg) but it has to be POST.

Is that possible? Any links for me?

Thanks!