I'm not sure it it can be done via firmware but I know that it can be done via software.
AnyDVD has many useful features invluding controling the reading speed of your drive.
- Works as a driver automatically in the background>
- Removes encryption (CSS) and region code (RPC) from DVDs>
- Removes analogue copy protection (Macrovision) >
- Removes prohibited user operations like forced subtitles and other limitations >
- Decrypts WITHOUT having to save the data onto the hard disk>
- Decrypts "on the fly">
- Prevents launch of software from your Video DVDs (e.g., PC-Friendly)>
- Allows setting of your vertical refresh rate depending on the video material>
- Allows execution of programs on disc insertion and removal> [li]Allows speed control of your DVD drives[/li]>
- Works with all DVDs>
- Works with all DVD-drives, no matter what region code it has>
- Works with every DVD copying and player software (e.g. CloneDVD) >
- Works transparently for the operating system: DVDs can be shared over the network, they can be copied with the command prompt or with Windows Explorer, etc.>
- Proven to be stable and fast, does not need an ASPI driver>
- New Feature AnyCDDA: play, copy and rip protected Audio CDs!>
If you do not need the features of AnyDVD I think CD Speed can do it as well.