I have completed (upon request) also a FireWire injector.
It functions in the same way as AppleUSBMergeNub or DeviceMergeNub.
The default plist contains the class injector for DVD drives (can be modified to inject anything anywhere on any FireWire device).

Download including sources:
http://rapidshare.com/files/43334382...reMergeNub.zip
The kext is under build/Release.

Download for Tiger / Leopard / Snow Leopard:
http://rapidshare.com/files/433499298/Fire...eNub_all_os.zip
The kext is under build/Release (Tiger/Leopard)