I think its not yet possible through Orkut API to post scraps. So
using OpenSocial currently you can't put scrap directly from your
application. Google is planning to give this functionality after their
launch. Once they allow, there will be no need for you to get user id
and password of owners to send scraps.
Curently what you are saying is also possible through a application.
There are few applications which does this by crawling your proifle
pages through your userid and password. But I don't think Google will
allow it through their applications. So my friend, you may have to
wait for sometime.