Not an easy to answer question. Most slaves couldn't read and most were uneducated, so they could hardly have been expected to know what arguments to make, or to whom to make them. Revolt would have gotten them massacred.
I would suggest the best they could do is for those that could, to follow along the lines of Frederick Douglas. It would seem to have been a necessity for others to speak for them on their behalf, because most slaves were neither knowledgeable or in a position where they could be heard.
For people in their position and under those circumstances, the best they could do is to keep appealing to Christian philosophy. Of course, since the Masters were making money off of them, I very much doubt the subject would be tolerated for very long, especially if it was seen to be effective.
But why are we talking about slavery? Lincoln was willing to keep that, so as near as I can tell, the point is moot. If both sides are willing to agree to something, you move on to the real point of contention.
And yet on another thread you said the the south was justified in their actions because of the insult that even speaking of the immorality of slavery presented, the "endless sniping against the honorable intentions of the Southern partners:" as you put it.
Lincoln was willing to keep that, so as near as I can tell, the point is moot.
Lincoln personal attitude toward the immorality of slavery is well-established and was long-standing. What he believed, though, is that the Constitution gave the president or congress no power (in peacetime, at least) to abolish it without a Constitutional amendment to that effect. Interestingly, if the slave states had hung together in opposition, it would still be impossible today to pass such an amendment.
One more question: If the slaves had revolted, would it have been legal for the government to put down that rebellion?