That would not be something that you can config on POL itself. As I'm sure you already know, POL using the swap file during normal operations can basically be a shard-killer, causing noticeable lag hiccoughs.
Basically, the only solution is to get more memory on the server and/or reduce the number of 'memory hog' applications you may have running on the server. As a 'real-time' game, POL is really going to do best when it is the primary application running on the server, as far as allocation and use of memory.