This was another idea that someone sent me. Granted I don't know much about the Abolitionist movement in England.
I'm thinking the CSA surviving is too much of an overdone wank, personally. If you can think of a unique/creative way to make it happen (other than simply 'UK INTERVENTION B/C UK IS DA BEST'), I'd go for it. Other than that, a TL where the CSA -doesn't- survive, but rather the ACW is a Pyrrhic victory for the Union (such that they're too weak to enforce Reconstruction, etc.).
A POD during the 1820s or something would be best, gives enough time for the South to build up proper strength and build alliances. Could have some OTL legislation pass, some not. Could have more foreign direct investment in the South by the Brits (in the case of a much more reactionary Great Britain---another POD idea).
Alternately, have the Brits never outlaw the Atlantic Slave Trade (by Abolitionist MP William Wilberforce, 1807 I think---have him die of his gastroenteritis or whatever he had), and the abolitionist movement dies in its cradle, pushing worldwide abolition movements back several decades (and thus push back the ACW, or at least make it not about slavery and more expressedly about states' rights---more states may join the secessionists in opposing the oppressive federal government).
Alternately still, or additionally, have a bigger domestic push against conscription in the Union such that their forces are significantly hampered or otherwise occupied putting down revolts in the North, allowing the South to gain more ground more quickly. This, combined with the previous two would be my choice for having the CSA survive. A reactionary Great Britain that has not yet outlawed slavery (something happens to twist moralism in the US, too) that's more willing to invest in the South (military investment most importantly, possibly help industrializing), plus a more unstable North, minus the moral highground of the Abolition Movement.