OTOH, I don't want to just install the prerequisite modules because
  coda itself might fail to build, and then the installation is surely
  inconsistent.

Sorry, I didn't follow what you were trying to do.  I just do
build/install of each package in the chain.  If the .so version
changes, then the old one is there, and if not then it must be ABI
compatible (right Jan??)...  I haven't lost from installing new
lwp/rpc2/rvm libraries - all the pain is in venus anyway.  But
seriously, I know that's living a bit dangerously, but tarring up of
/usr/local/coda goes a long way to be able to back out.

You might also try building .debs in a chroot.  I build packages that
way on NetBSD (pkgsrc/pkg_tools/{pkg_comp,pkg_chk} automate most of
this).

  I'm pretty sure that the --with-lwp-includes option and friends are
  exactly what I need.

You'll also need to get libtool to link against the .la from the
source tree, and then repoint them on install, I think, to fully get
what you want.