Sourcing one spec from another permissible?

[Richard Shaw]

NOTE (just for Jon :): This is for RPM Fusion but the question is a
technical one.

I'm looking at packaging zfs for Fedora (via RPM Fusion) and it has a
single source package but contains two spec files. One for the
utilities (zfs{,-devel,-dracut,-test}) and one for the kernel module
(zfs-modules). The one for the kernel module is a mess of macros and
I'd rather not keep it inline with the main spec that I've gotten nice
and clean/readable.

The only other solution I know of is to create two SRPMS which use the
same source, which I don't like. They may not use any common files so
I guess I could split the source archive but that's not a very clean
method either.

Is it technically possible to "source in" an spec from within a spec?

If so, is it permissible?

Thanks
Richard