I had the same problem and managed to generate a rpm from src.rpm that installs the cluster locking library.
These are the steps I have followed:
* install the src.rpm, in my case "lvm2-cluster-2.02.16-3.el5.src.rpm"
* modify the spec file:
** eliminate this option "--enable-static_link" so that it allows shared library creation
** change this option "--with-cluster=internal" for "--with-cluster=shared"
** include in the %files section the libraries generated:
** change the man file name in the %files section:
as it expects somewhere the non gzipped version
* once saved the spec file instruct a "rpmbuild -bb "
* install the generated rpm which should have the same files as the binary one provided with the centos5 distro plus the .so libraries
I have still not tested it, so I cannot tell if it works. Hope it helps though.