Is it possible to split an export into two or more .dmp files?
Yes it is. The Oracle export utility lets you specify a max file size for your dump files. This is done with the FILESIZE parameter. You can enumerate multiple files with the FILES parameter. If you need more files than you enumerated, the export utility will create files for you. For example:
exp userid=system/manager full=y files=full_001.dmp,full_002.dmp,full_003.dmp filesize=20000000
The above will limit files to 2 million bytes. The export utility will write to full_001.dmp first. Once that file reaches the limit, the export utility will write to full_002.dmp and so on.