Moving to innodb_file_per_table?

I have just noticed (unfortunately while trying to restore from backup), that on my production server there is a 35GB ibdata1 file! As I understand I can reduce its size by moving to innodb_file_per_table. However following the answers I have seen here (link below), you have to dump and drop all databases before you can start the conversion. How long would it take to do this convert? Is it possible to stagger the convert and do it one database at a time? Thanks. https://dba.stackexchange.com/questions/8982/what-is-the-best-way-to-reduce-the-size-of-ibdata-in-mysql