Once soyuz is managing distributions properly, the lack of a sourcepackagename in a distribution is an explicit indication that the sourcepackage is not in the distribution and thus it makes no sense to file a bug against it, none at all.
I'm not sure if such an elaborate solution as you describe is worthwhile in the short term, but perhaps others will disagree with me.
Once soyuz is managing distributions properly, the lack of a sourcepackagename in a distribution is an explicit indication that the sourcepackage is not in the distribution and thus it makes no sense to file a bug against it, none at all.
I'm not sure if such an elaborate solution as you describe is worthwhile in the short term, but perhaps others will disagree with me.