I sometimes use the feature \'Reconcile Offline Work...\' found in Perforce\'s P4V IDE to sync up any files that I have been working on while disconnected from the P4 depot.
I'm looking for a .p4ignore like solution as well (and not one tied to a particular IDE). Thus far, the closest thing I've found is p4delta. It sounds like it will do exactly what the original poster was asking, albeit through another layer of indirection.
http://p4delta.sourceforge.net
Unfortunately, while this does seem to produce the proper list of files, I can't get "p4delta --execute" to work ("Can't modify a frozen string") and the project has not been updated in year. Perhaps others will have better luck.