Well it really depends what kind of drive you get. You probably can't power the drive off 1394 or USB since the current is very limited ~200mA @ 5V I believe. Your average optical drive needs both 12V for motors and 5V for logic.
You're more likely to succeed using a slimline/laptop drive which will probably be designed to run off 5V at reasonably low current, still probably not USB.
Easy solutions are to run an extension from your molex connector at the back to the front as you said, or you could use a couple of linear regulators to get the voltages you need from an accessory line under the dash. The 12V line probably should be regulated down using a low drop-out regulator so that when the car's running the drive isn't getting noisy 14v and causing the drive to go into overdrive. 1A regulators are probably what you need, with appropriate heatsinking probably required on 5v. The LM317 is the standard regulator to use as it's adjustable and simple to use, only need a couple of resistors and capacitors... If you want to go down this route I can probably help out. I made a separate power supply for my cdrom since my carPC only had an Ituner PW60 back then.