It's not enough. The Confederacy was pretty much dead all over when Lee surrendered. Worst comes to worst the US starts shipping Southerners to various deserts out west.
Anyone who wants to explore a continuation of the War Between the States under any scenerio has to read "An Honorable Defeat: The Last Days of the Confederate Government" by William C. Davis.
Confederate victory could have most easily been won in two points in time.
First, after First Bull Run if the Southern command had followed the fleeing Federal forces into Washington City and captured Lincoln and the Capital Building and the War Department, it would have been over. Maryland and Kentucky would most likely have joined the Confederacy within thirty days.
Second, if Lee's Special Order191 had not found it's way into McClellan's hands at Antietam, his Army of Northern Virginia could have crushed the Army of the Potomac and had a clear path to the capital of Pennsylvania, Harrisburg. From there, a British/ French political intervention would have been very likely. Not guaranteed, but believeable.
Other than that, and after that, the North just kept getting stronger and stronger and the South had no realistic chance of winning any critical victory. The best it could have done is to accept Lincoln's offer made on Grant's command boat at Hampton Roads, VA in February, 1865 to give up any claim to slavery or secession and receive compensation for the slaves value.
Now, I'm not sure Lincoln could have gotten that approved by Congress, but it would have been a better result even without the compensation than the years of Reconstruction that resulted from the Abolutionist Republican Congress in the Original Timeline.