I found the answer on how to do this:
1) Download the source for the latest version of grub2 from git:
git clone git://git.sv.gnu.org/grub.git cd grub
2) Graft the "grub-extras" source code into the grub2 source tree:
git clone git://git.sv.gnu.org/grub-extras.git
3) Edit autogen.sh to add grub-extras into the build by adding this:
export GRUB_CONTRIB=/<absolute pathname to>/grub/grub-extras
4) Now build grub2 as you normally would:
./autogen.sh ./configure make make install
-- Thats it!