The default qmail as supplied with Plesk uses the FIRST IP address configured on your server if you have more than one (e.g. If you have eth0:0, eth0:1, eth0:2 then qmail will use the IP defined in eth0:0)
You can therefore have SOME control by changing which IP is defined in eth0:0. For example, if you want to use the IP that's currently in eth0:1 then simply swap the IP addresses between the two in /etc/sysconfig/networking-scripts/ifcfg-eth0:0 and eth0:1 (in Centos -- not sure about other OSes). You would then need to reboot or at least restart the network service (# service network restart). Also note that if you have a VPS then your changes may not survive a reboot and you may need to speak to your VPS provider to see if they can help.
WARNING: Although I've done such a swap myself in the past in Plesk 7 or 8 (it was a long time ago) it might screw things up in Plesk 10.x for all I know. So do so at your own risk, especially with later versions of Plesk.
What tkalfaoglu is requesting is that the patch for qmail that allows much more comprehensive control to be integrated in the version of qmail supplied with Plesk - down to defining which IP is used for which domain. And I'll second that request with bells on.
Unfortunately Postfix is now the default MTA for Plesk as of 11.x and I suspect we might be out of luck.
Personally I love qmail.