MTU 9000 _before_ rootfs-mount

[C-Otto]

Hello!
I am a proud owner of two gigabit-cards (Intel, e1000) and used the chance to make a diskless client with the root-fs being NFS over gigabit.
That systems has been working flawlessly for two weeks now, but I miss a little piece of performance.
The card is capable of jumboframes, that is a MTU higher than 1500 (which is the standard). I can change the MTU using "ifconfig eth0 mtu 9000", but this causes many problems, if I don't change the server's MTU the same time. When the server has a MTU of 9000 and I reboot my client (with MTU 1500, because it is the default) I get several NFS-errors (because packets get dropped or chopped or something, which is quite obvious).
Now my question:
Is there a way to set up a MTU of 9000 _before_ the kernel mounts the root-fs? I use dhcp to get my IP and I found out there is a method to specify the MTU, but the kernel does not care about that. I also tried patching the e1000-"module" (it has to be inside the kernel), but it fails changing the MTU (at least in the places I placed the line in the code).

Thanks, C-Otto