The delegates from South Carolina, Georgia, and other Southern states had demands that were deal breakers if they were not included in the Constitution so I do not believe that abolition would have been possible. If you read the Constitution there are 3 sections that have to do with slavery, but they do not directly mention the words "slave" or "slavery". The words in those sections are very carefully crafted. I find this analysis done by Frederick Douglass to be very insightful:

I hold that the Federal Government was never, in its essence, anything but an anti-slavery government. Abolish slavery tomorrow, and not a sentence or syllable of the Constitution need be altered. It was purposely so framed as to give no claim, no sanction to the claim, of property in a man. If in its origin slavery had any relation to the government, it was only as the scaffolding to the magnificent structure, to be removed as soon as the building was completed. There is in the Constitution no East, no West, no North, no South, no black, no white, no slave, no slaveholder, but all are citizens who are of American birth.

The clause dubbed the "Fugitive Slave Clause" was originally phrased as:

Person legally held to Service or Labour in one state

was changed amended to

Person held to Service or Labour in one state, under the Laws thereof

The new phrasing specifically placed the law within slave holding states so that it would not apply to escaped slaves in states where slavery was abolished or in Federal land.

Another thing to look at was the 3/5s compromise. The Southerners agreed to it so they would not have to pay more taxes in regards to their population census. The 3/5s compromise gave more governing power to the non-slave holding states by giving them more seats in the house and more votes in the Electoral College.