Replying to myself...
> Probably the easiest option here is to simply prepend the desired
> directories onto the GUILE_LOAD_PATH environment variable before calling
> scm_boot_guile.
On second thought, this is probably not a good idea, because you don't
want this setting to propagate to other subprocesses. This is probably
the best thing:
> SCM var = scm_c_lookup ("%load-path");
> scm_variable_set_x (var, scm_cons (scm_from_locale_string (dir),
> scm_variable_ref (var)));
Does that work for you?
Mark