I've done that in the "old" way...
after several months searching, here's a tutorial of what I've done:
1. make an image of the first install disc (disc utility, as DVD/CD master)
2. eject the disc image
3. you need to stretch that image into the size of the DVD
3.1 stretch the image size (from 650 to 4.39GB)
terminal:
hdiutil resize -size 4.39g -imageOnly /volumes/... (throw the dmg here)
3.2 stretch the partition size (from 647 to 4.37GB)
terminal:
hdiutil resize -size 4.37g -partitionOnly /volumes/... (throw the dmg here)
4. mount it, change its name (if you want to), adjust the folder positions (visually), copy the installation packages from the other install CDs into the folder /system/installation/packages (overwrite the ones that are already there)
5. edit the installation settings:
go to the main install pref (/system/installation/packages/OSInstallCache.plist)
open with text edit:
remove the location flag of the packages that point to other install discs (ex: <key>IFPkgFlagProxyPackageLocation</key>
<string>disc://Mac OS X Install Disc 3/Packages/X11User.pkg</string>
you need to remove those flags completely
6. you can add more installation programs, because the DVD is big enough
7. toast: mac volume, mount image, don't optimize
DAO, 4x, DVD-R 4.7GB, closed (of course you can test it with a DVD-RW, it works as well and if somthing is wrong, you won't spend any DVD-R)
8. reboot, press C
test it!