Distinct conjunctions for subordinate clauses in different case relations to main clause

Most of the languages I'm familiar with have just one conjunction
to introduce a subordinate clause, whether that clause is the
subject or the object of the verb in the main clause.  E.g.,

It's interesting that you mention that.
[= "you mention that"-NOM is interesting]

He didn't know that you were coming.
[He-NOM know-NEG "you were coming"-ACC]

English also has another conjunction "whether"
to introduce subordinate clauses with non-indicative
mood (if that's the right term).  Esperanto behaves
roughly the same way with "ke" and "cxu", except
that it doesn't require a dummy subject in the main
clause when the ke/cxu subordinate clause is
the subject of the main verb.

Estas interese, ke vi mencias tion.

Li ne sciis, ke ve venos.

In gjâ-zym-byn I recently decided that the old way of
introducing a subordinate clause that's the subject
of the main verb or head of an adjective was clunky,
and I needed a new conjunction.

zqe  miq-i  huw-fwa    nxiqn-i, hoqnx kq ty-o    runx-zox ler tq tu-i.
this TOP-at happy-CAUS CMT-at   that  1  home-to go-V.ACT FUT 2  AGT-at

Estas felicxige, ke vi venos al mia hejmo.

It makes [me] happy that you are coming to my home.

This required a dummy forward-reference pronoun "zqe"
in the main clause to be the topic of "huw-fwa".  I added
"dxoqnx" as a conjunction syntactically similar to "hoqnx",
but a clause introduced by "dxoqnx" is the subject (usually topic)
of the main verb while a clause introduced by "hoqnx" is
the object of the main verb (usually object-of-perception
rather than patient or result).

E.g.,

huw-fwa    nxiqn-i, dxoqnx kq ty-o    runx-zox ler tq tu-i.
happy-CAUS CMT-at   that   1  home-to go-V.ACT FUT 2  AGT-at

means the same thing, but is terser by several syllables.

Do any natlangs y'all know of have a similar distinction
in their subordinate-clause conjunctions?  Can you think
of other case-role distinctions that might be made in
clausal conjunctions?

(This isn't in the online gzb grammar yet.)

--
Jim Henry
http://www.pobox.com/~jimhenry/esp.htm

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