It should be possible to get the SDK, the kernel sources with nokia pathces and recompile the whole kernel with exactly the config the firmware kernel has. Then you could enable additional modules in the config unless they do not require additional functionality compiled into the kernel to work (that of course would trigger a recopile of the whole kernel with a different kernel as result compared to the firmware kernel).
However, I succeeded in doing this for additional iptables modules (which do not require any additional changes inside but to be enabled in the config), i also succeeded in building a nfs module once, however i never used it (just enabled it to be build as module so i don;t have to do it again if i would need it).
As the new Firmwar image is out I'll have to rebuidl my custom modules anyway, if i get a nfs module fitting to the firmware installed kernel, I'll post it somwhere and let you know here. But might take up to a week until i'll find time.

Btw. if you want to do it yourself, all i needed to get the SDK with the kernel sources setup for compilation was the SDK install howto and the Kernel howto (both somewhere on maemo.org).