Depends how large the Oracle export file is.
You could always restore the file into a filesystem on box3 and then use NFS to mount that drive on to a filesystem on box2.
NFS is simple enough to use, depending on your flavour of UNIX there will be a nfsconf file with all the the network files, in HP-UX it is in /etc/rc.config.d/. The entries in here are self explanatory - box3 will need to be a server and client. Create an exports file on this box to detail what directory you want to export, and then simply use the exportfs command to export.
Modfiy the nfsconf file on box2 to make it a client. Start the nfs sub-system on box3 by locating the start script, which will be with all the other networking start scripts, in HP-UX this is /sbin/init.d/ - if you're unsure where it is all these scripts are linked to the run level scripts in rc1.d/rc2.d/rc3/d etc.
Then start nfs on box2. Make sure you do it in this order - the server needs to be started before the client or else the client will hang while it looks for the nfs server.
The syntax on box2 then, to mount the exported filesystem is a logical extension of the normal mount syntax:
mount [nfsserver]:[exported_directory] [local_directory]
Having said all this, attention must be made to network impact, if the export is very large, exporting the directory will put a consequent strain on the network and you may become very unpopular very fast.
If this isnt an issue run man pages on nfs and exportfs to get a better picture if you're stuck at any point.
Hope this helps.