Best practice: Find closest package server in DS

Setup: We have around 10 branch offices world-wide, and workers who travel in between them. We have only one central DS (ver 6.9.164), but a PXE/package server with a replicated copy of images and software packages on each site. So far we have set the %SITE% property manually on each machine, but is there an easy way to find the local package server and map a drive to it? Preferably, we would like to update the %SITE% property (which is also available from Properties->Location in the DS console), since all our deployment jobs refer to it. Anyone?