For a timeline on exactly this, see
The Black and the Gray by Robert Perkins.
Historically, Jefferson Davis did throw his support behind such in late 1864 and got Lee to come out publicly in favor of it too, with the first units drilling in Richmond right before the close of the war. Of note in this same vein, in early 1865 the C.S. did dispatch a diplomatic mission to both London and Paris seeking recognition in exchange for
full emancipation. See
Blue and Gray Diplomacy: A History of Union and Confederate Foreign Relations by Howard Jones, Chapter
Requiem for Napoleon—and Intervention -
Yet Kenner’s secret mission was anything but secret. Reports about it appeared in the Richmond Enquirer and Sentinel in late December 1864. Seward notified the Union embassy in London of the mission on January 10, and the news appeared in the Paris press on March 2. Kenner had left Richmond in disguise on January 18, 1865, lamenting that he would have had a better chance in early 1863, when both England and France were well aware of the Confederacy’s diminishing resources and the battles at Gettysburg and Vicksburg had not yet occurred. “I would have succeeded” in securing a £15 million loan when “slavery was the bone of contention.”
Now, neither Napoleon nor Palmerston showed interest in the proposal. To Kenner and Mason, the emperor explained that he refused to move without England and that he “had never taken [slavery] into consideration” regarding recognition. On March 14, 1865, Mason met with Palmerston for more than an hour at Cambridge House, where the prime minister also rejected the plan, insisting that slavery was not the obstacle to intervention; the Confederacy had not proven its independence on the battlefield. The Richmond Dispatch glumly noted, “No one would receive us as a gift." The responses should not have surprised the Confederacy. Napoleon’s reply contained nothing different from his initial determination to follow the British lead. Palmerston’s argument against recognition correlated with his long conversation with De Leon in the summer of 1862. On neither side of the English Channel did slavery emerge as the critical consideration.