If by clustered you mean in a High availability mode, then all you would need to do is create a separate proxy port and not create a port redirect for it.
The only traffic that will be load balanced in this situation would be traffic going to port 9090 as a port redirect has been configured for this port. Ports 9091 and 8080 will not be load balanced and will only stay on the appliance.
Balancing the two servers is half the traffic headed one and the other half by the other, but I want a unique website that uses port 80 only comes out of the appliance by a
The only way I could think of pointing a specific web site to a non load balancing proxy port would be to use a Pac file in combination with the settings above.