No need to replace the kernel.

Install the "rx-34-kernel-nfs-modules" package. I don't remember which repository it is in, but it is one of the main ones. No doubt you'll need red-pill mode enabled to do this.

You'll need to insmod the modules yourself. Also, with previous firmware versions, the mount command in busybox was crippled, and needed to be replaced, but it seems to work in the latest release. You'll also want to install portmap, or mount using the "nolock" option. You can also install rpc.statd if you want (from the nfs-common package), but this probably isn't important for you.

There are a few older threads about this from back a few months. Try searching for them if you want more info.

/Lon