You might be able to increase the "swappiness" of your processes using cgroups - See: Documentation/cgroups/cgroups.txt. cgroups are control groups, via which you can give families of related processes specific characteristics. Section 1.6 of that document shows how to set up such a group.
Having established a cgroup you can set it's swappiness (ie. how soon the kernel will start swapping it relative to other processes in the system). See: Documentation/cgroups/memory.txt.
Disclaimer: I have not had occasion to use this function yet so the above is from glancing through these documents. You'd better read them carefully before you try to use them!