FreeBSD PF rdr load balancing question

[Roman Vasilyev]

Hi,

my company using openvpn with UDP transport on SMP machine, currently we 
using Linux as server platform. So for more effective CPU usage we're 
running openvpn instances which equals to CPU count. For load balancing 
we using iptables with simple rule:
iptables -t nat -A PREROUTING -p udp -m state --state NEW -m udp -j 
REDIRECT --to-ports 8041-8048 --random

We are moving to freebsd, and I want to use best firewall PF, I didn't 
found any ability for load balancing by ports only IP's, my question is:
what's the best way to have load balancing by ports on LOCAL machine 
with PF?