"Substitutes:" in project conf only working for build dependencies?

What about runtime dependencies?

Debian 6 has no installation candidate for libgmp, so I added

%if 0%{?debian_version} == 0600
Substitute: libgmp libgmp3c2
Substitute: libgmp-dev libgmp3-dev
%endif

to the project config (“home:kalium:test”). However, OBS still complains about missing “libgmp”.

?