Migrating from MyISAM to INNODB while minimizing downtime

I need to migrate two 5GB MyISAM tables to Innodb tables. What’s the best way to do this while minimizing downtime?

It takes several hours even on a quad proc 8GB RAM box to load a 5GB MyISAM mysqldump as a INNODB tables.

And this is with several optimizations including these:

-Increasing the innodb_buffer_pool_size to 4GB

My questions:

  1. What other performance optimizations can I perform?
  2. How do I do this to minimize downtime. What I was thinking is that I’d take a mysqldump, copy it to another server and import the database tables as Innodb tables.

Once the import is complete, I would do a diff between the previous mysqldump and the current live database, copy and import the diff into the other DB Server.

Is this possible?
I was looking online and could not find a way to do this “diff + import only the diff” thing.