substitute for skos:isSubjectOf

The SKOS Primer recommends using dc:subject for indexing purposes. For
the inverse relation - this concept "is subject of" or "indexes" that
resource - it gives no recommendation. The discussion about indexing
properties in SKOS (commendably summarized in
http://www.w3.org/2006/07/SWD/wiki/SkosDesign/Indexing) also paid no
attention to the now vanished skos:isSubjectOf. 
 
But it's definitively missing. My use case is this:
 
On the upcoming RDFa-enriched web pages for the Standard Thesaurus
Economics (maintained by the German National Library of Economics, ZBW),
we will include links to library resources. This links trigger a search
for the concept at hand in the subject index of the library database -
e.g. 
http://www.econis.eu/DB=1/LNG=EN/CMD?ACT=SRCHM&IKT3=46&TRM3=Black+market
searches for the concept http://zbw.eu/stw/descriptor/19289-4 with the
prefLabel "Black market" and returns a result page with further links to
books, articles and so on (not RDFa-enriched up to now, but this could
change). To enhance the Web of Linked Data, I want to express this
relationship in RDFa also. A triple
 
http://zbw.eu/stw/descriptor/19289-4
<http://zbw.eu/stw/descriptor/19289-4>  skos:isSubjectOf
http://www.econis.eu/...=Black+market 
 
would have been perfect. (Of cause, the inverse relation can be
expressed easily by dc:subject, but that puts the descriptor in the
object position.)
 
I understand that the missing relation may be, strictly spoken, not part
of the KOS (but an application of the KOS to resources) and therefore
may be outside the scope of SKOS. But nevertheless a substitute is
required. 
 
It would be easy to define some custom property, e.g. zbw:indexes, with
skos:Concept as domain and rdf:resource as range. But since I feel that
this may be a requirement not only by our site, there should be a more
common, standardized way.
 
I did some research on this, but was out of luck:
 
- dc:subject lacks an inverseProperty
- sioc:topic dito
- dcterms:references/dcterms:isReferencedBy seems to be aimed at
citations and alike
- ore:describes/ore:isDescribedBy is too restricted in Domain/Range
(ore:ResourceMap/ore:Aggregation)
- rdfs:seeAlso is too general
- frbr:isSubjectOf could be fine if domain and range are sufficiently
general, but I couldn't figure out the status of this one (it is
described as a skos:Concept in
http://sandbox.metadataregistry.org/concept/show/id/923.html, but is not
part of http://purl.org/vocab/frbr/core or
http://purl.org/vocab/frbr/extended <http://vocab.org/frbr/extended> )
 
I'm convinced that terminologies - expressed in SKOS - could perfectly
serve as hubs in a Web of Linked Data. To this end, it would be highly
beneficial to figure out and recommend a uniform way to link from
skos:Concepts to arbitrary other resources. Can we do this?
 
Kind regards, Joachim