Outbound NAT port change problem

[FretTapper]

Ok, I'm trying to setup a case where I can query a dns server on the outside world over one of my two WAN connections explicitly.  I am trying to use outbound nat to say any activity on port 45150 should be sent out one interface and translated to port 53, and any activity on port 45151 should be sent out on the other interface and translated to port 53.  Here is my outbound setup:

WAN    any  *  *  45150  10.10.5.1  53  NO
WAN2  any  *  *  45151  10.10.10.1  53  NO

…I suppose the possible answers to my query are:
1.) You can't do it
2.) You have it setup wrong

...anyone wanna help me?  Thanks in advance.