You would need both changes in Black and White thought for this to be possible. The mainline thought of both blacks and whites during the Civil War / Reconstruction period was basically intergrationists. This logic would inevitably be subverted by the white south, because it would produce decreasing returns for the all important white majority as time went by...(a white majority which a dispersed black populace would remain heavily reliant upon for protection.)
For economic reasons which would be hard to surmount, a Black state, or black reservations were never considered. However, if the ACS (American Colonization Society) philosophy could have been morphed into some sort of black state philosophy, under the U.S. Constitutional Framework, you might have been able to defer or even delete the Southern Redemption.
Not sure this would have been better in the long run, but you'd have to have some force, and some place, both northern white republicans and black freemen though blacks could move to...and have this place be politically strengthened...at least in the house and probably in the senate as well...by racial consentration.
It might have led to some sort of final solution elswhere, but it's be harder to effect a historical "Southern Redemption" if, say, Republicans had decided to ammend the Constitution to make Mississippi a Fremen's State or something like that. Either way, both white Radical Republicans, and Black Freemen, would of had to have viewed blacks themselves less as citizens but more as northern clients for such a scenario to work, as its the only scenario in which the military force required to resist the whites of the south could have been developed and maintaind from the black populace principally.
I.E., blacks in this country would have basically had to become Maroons.