I did a bunch of research into this because I had a client that wanted to use php5. After reading countless upon countless of thread, I determined it was possible, if you did it the right way
I use PlatinumServerManagement.com to help me in new server setup/lock down, troubleshooting critical issues (sometimes of my own doing), and they were able to get this configured and running in about 10 mins on my server, with no downtime what-so-ever. I have the normal php using the .php exention, and still being updated by Cpanel, and I have php5 running on the .php5 exention.
I dont get any kickback for recommending them, so this is just a straight up, if your looking for someone to do it, they know how tip.
Z