There isn't a way without modding it.
Follow the instructions by Liam1080
http://forums.afterdawn.com/thread_view.cfm/117041
Then you need to buy the swapmagic disks 3.0 (DVD version and CD version)
http://www.swapmagic3.com/
Insert your swapmagic disk (Cd version), wait for it to load, swap in cd-r, hit circle or x on controller pad, and your cd-r should boot up.