Rinya cases

Hello all.

Okay. I've got a serious case problem. My Rinya is
ergative. As you know this means it marks semantic
roles instead of syntactic functions. Now I've reached
the point where I noticed that I could distinguish
between actions that are volitional and those that are
not by using different cases.

In intransitive (itr) sentences this is not a problem.
I either use the ergative case, which marks the agent and that
the action is made on purpose), or the absolutive case
(in most cases the subject of itr sentences is patient
or experiencer) which marks that the action is done
involuntarily.

Now to the real problem. Transitive sentences with verbs
of which the subject isn't the agent. To show that that
the action is non-volitional the "subject" should be marked
with the absolutive case. But then what happens to the
"object"? I can't use the ergative for that.

I'm thinking of introducing a new case to mark the
Influenced Object/The Experienced, OBJECTIVE.

Example:
"Will looked at a mouse."
Will is agent, he deliberately looked at the mouse.
He was acting. Will = Erg. ; Mouse = Abs.

"Will saw the mouse."
Will is the experiencer, and mouse is the experienced.
Will didn't act, he just happened to see the mouse.
Will = ABS. ; Mouse = OBJ.

Note that I want to have the same verb in both sentences
and don't want to inflect the verb (as e.g. Teonaht does).
I want to show the semantic roles just using different
cases on the noun phrases.

Thus:

Agent = Ergative
Experiencer/Patient = Absolutive
Recipient = Dative
Instrument = Instrumental
Influenced Object/The Experienced = Objective ??

Am I missing something here? What is the "normal" way
of doing this? Comments, please.
Perhaps the wrong time to ask this when most people
seem to be no-mail. Especially the king of ergative
case, Nik Taylor.

Daniel Andreasson
http://conlang.nu