Vista Remote assistance ports with Gateway-LAN firewall

How can I tune Remote Assistance on Vista in order to use permanently
the same port as on the previous version was 3389(RDP)?

I am trying to setup the Gateway-firewall-proxy for working with the
new Remote Assistance on Windows Vista.
What is changed from the XP version is that when activated, after
having created the request, the service keeps listening on randomly
choosen ports such as 50111 or similar 5xxxx (also defined on the
request File). So it would be needed that the firewall accept packets
within a certain range, and that would surely open too many ports on
our firewall.


Examples:

Request with XP
<?xml version="1.0" encoding="Unicode" ?><UPLOADINFO
TYPE="Escalated"><UPLOADDATA USERNAME="utente"
RCTICKET="65538,1,192.168.111.4:3389;xppro-en-vmware:
3389,*,I7uts43ZRQLcQRO0zTsTzo+cc1RvZEDMbvKHrzoQ6Qg =,*,
*,IFSDeiDo3YAGpwOkpnDhlG7vWUA=" RCTICKETENCRYPTED="0"
DtStart="1184076154" DtLength="60" PassStub="" L="0" /></UPLOADINFO>

Request in Vista
<?xml version="1.0"?>
<UPLOADINFO TYPE="Escalated"><UPLOADDATA USERNAME="myuser"
LHTICKET="ED8F629B40982"
RCTICKET="65538,1,192.168.111.1:49710;172.16.0.1:4 9711;172.16.152.1:49712,*,iCbY8R/
0XdAlYj7+xtyhhtJ2qLDH4vsUVTU2YHgylDRugslXIgVzF4/S2ao1sbeZ,*,*,
8s3AwWP59K8Db72FxfIqjqVUyRI=" PassStub="7T!1MeiXj*dzDp"
RCTICKETENCRYPTED="1" DtStart="1184075806" DtLength="360" L="0"/></
UPLOADINFO>


Thanks in advance
Andrea