You can specify the data directory using scripts (AFAIK you can't use a shortcut on Windows because it requires an absolute path to the .exe).
Shell script for Linux (make executable with "chmod a+x scriptname"):
Batch script for Windows (save as *.bat or *.cmd):
If you know how to do it, you can also apply gavinandresen's port/rpcport patch
or wait for it to be included in the official client (may take a while).