large MYSQL DB single file

I have a large MYSQL innodb database (115GB) running on single file mode in MySQL server.

I NEED to move this to file per table mode to allow me to optimize and reduce the overall DB size.

Im looking at various options to do this, but my problem falls in there only being a small window of downtime (roughly 5 hours).

1. Setup a clone of the server as a slave. Set the slave up with file_per_table, take a mysqldump from the main DB, run in the slave and have this replicating.

I will then look to fail over to the slave.

2. The other option is the usual mysqldump, drop DB and then import.

My concern is around the time to take the mysqldump and the quality of the dump being such a large size. I have BLOB data in the DB also.

Can anyone offer advise on a good approach?

Thanks