If you have the old 8 wire mod from modchips.com (the one that auto-ejects), then here's how you can boot DVD-Rs until you get the Messiah-J (on which I'll be reporting shortly).

1 Buy the largest TOC Original JAP DVD game (like DOA 2 or DMC)

2 Boot with this large TOC game

3 When the tray auto-ejects, swap in the DVD-R game wih smaller TOC

4 Tray auto-returns and the game boots if it is a good burn

Nice bonus.