Are the boost headers separately packaged under Fedora?

Looking at the boost-devel package, it requires the boost package of the same version. Here is what the boost-devel package requires:

$ rpm -qRp boost-devel-1.44.0-7.fc14.x86_64.rpm 
boost = 1.44.0-7.fc14
rpmlib(CompressedFileNames) <= 3.0.4-1
rpmlib(FileDigests) <= 4.6.0-1
rpmlib(PayloadFilesHavePrefix) <= 4.0-1
rpmlib(VersionedDependencies) <= 3.0.3-1
rpmlib(PayloadIsXz) <= 5.2-1

The boost-devel package is the only package that has the boost header files, and it requires the other packages, so the answer to your question is: No, there are no packages you can install that would only provide the headers. Fedora packages typically have their -devel packages require the other package that includes any libraries used to compile using the headers in the package, as is in this case.