Do not evaluate python_sitearch every time it's used. Override definition in /usr/lib/rpm/macros.
@@ -1,4 +1,4 @@
-%{!?python_sitearch: %define python_sitearch %(%{__python} -c "from distutils.sysconfig import get_python_lib; print get_python_lib(1)")}
+%global python_sitearch %(%{__python} -c "from distutils.sysconfig import get_python_lib; print get_python_lib(1)")
%{!?version: %define version %(cat version)}