Since it sounds like libfwCore.so.0 is supposed to be a private library so I think the correct solution here is for upstream to build the binary using an rpath rather than turning it into a public library placed in a different path.
I've already try something like : export DEB_LDFLAGS_MAINT_APPEND = -Wl,--no-as-needed -Wl,-rpath=/usr/lib/fw4spl -ldl But it doesn't work. Is it something like it that you were talking by "rpath" ? Corentin