iptables: Route outgoing requests to a local proxy preserving destination address and port

Question

I want the proxy to make some routing decisions based on the original destination IP and port. I can do this easily for an incoming request:

iptables -t mangle -A PREROUTING -p tcp --destination 10.37.253.90 \
--dport 8080 -j TPROXY --on-port 8081

This intercepts the packets headed for 10.87.253.90:8080 on local port 8081 of the proxy. But for an outgoing request, how can I do this?