After a quick search on the Perl DBI mailing lists, I found a question and its answer which seems to be the solution to my problem.

It would appear that if I want to use IPC then I need to configure a SID for the connection, but the answer that was provided cast doubt on whether IPC would be faster.

If I can get it to work, perhaps I'll report my findings. Each run of my app updates 20,000 - 60,000 entries in a 6,000,000 record database over 6 tables so any small performance gain should be noticable.