G'amah antipassive

I'm having to think a lot about my new language,
G'amah, with its ergative system... I've several
questions to ask:

1. The language is VSO, prepositional, rather
   analytical (just lots of clitics). I want to
   have an antipassive, which I mark with a prefix
   on the verb and a particle that stands in place
   of the demoted absolutive:

d'ul lli-nhach n'ana- hoh
eat  AD  cat   AI.DUP mouse
'the cat eats mice'

becomes

ad'ul    lli-nhach bu
AP.comer AD  gato  APO
'the cat eats'

APO means AntiPassive Object, but it's not clear whether
it's a meaningless particle or a resumptive pronoun
(the former is more likely, since it's totally
invariable).

So the first question wouuld be: is this setting
likely? Would a language like this use some other
periphrastic construction for the antipassive
(just as modern IE languages do for the passive?).

2. In langs with passive voice, the demoted subject
can be mentioned with an oblique complement. What
would happen with antipassive objects? Any natlang
precedents of such a construction? In that case,
what would its connotations be? (In passive voice,
the idea is to emphasize the object and making
the subject irrelevant -- what about antipassive?).

Thanks in advance to any who reply. (Yes, Nik and
David, I'm talking to you :). This is totally new
for me...


--Pablo Flores
  http://www.geocities.com/pablo-david/index.html
  http://www.geocities.com/pablo-david/draseleq.html