You could get the ppp source and build your own using the m68k-linux-gcc compiler supplied as part of the BSP(actually in the LinuxTools tarball). You could start with the ppp srouce in ftp://ftp.samba.org/pub/ppp/

I haven't personally built this, but it shouldn't be that hard. Remember that you need to configure with the target compiler(m68k-linux-gcc) since you want to create code that will *run* on the target.

the root filesystem is build using the tree found in romfs/.romdata, so you could create the files, and then install them into that directory, and then from the top-level execut "make images" to recreate the root filesystem image...

I started to look at the ppp package shipped as part of standard Linux distributions, and unfortunately it is not set up for cross-compiliation. It assumes that a native compiler exists for building teh daemon.

You could try extracting the user/pppd directory out of a aClinux distribution and modify as necessary to get it to build for you.