[me] Lincoln, I assure you, could have said plenty...
[thee] Like what?
Like, endorsing explicitly the proposed Thirteenth Amendment idea during the campaign, and endorsing Popular Sovereignty below a certain latitude as part of the amendment, to allow the South a certain room to expand in (they hadn't run out of room yet in Texas, and there was still the Indian Territory on the horizon).
Anything Lincoln could have done to alleviate the correct (as it turns out) impression of the Southerners that he was mounting a jihad of total war with no compromises against them, would have gone a long way to defusing sectional tensions.
But my modest proposal assumes that your appreciation of Lincoln's intentions toward slavery in the South is correct, and that his statements during the campaign about limited objectives weren't just rhetoric.
Lincoln intended all along to free the slaves and give them the vote -- making them the masters of the South.
Your modest proposal also displays a lack of understanding of the history of the period. Lincoln couldn't endorse the 13th Amendment - it hadn't been proposed yet. The amendment was rushed through the Congress in February 1861 in an attempt to head off the southern rebellion. It would have been hard for Lincoln to campaign for something that hadn't been proposed yet. Lincoln couldn't have done anything to halt the spread of slavery in Texas since Texas was already a slave state and could promote slavery anywhere within her borders. In short, there was nothing that Lincoln could have done to prevent the southern actions except lose the election.