Personally, I don't think it can be done effectively. The two settings are deeply incompatible. There is no effective way to make the standard form of Outer Planar travel be ships through a medium where the major factions are the Elven Imperial Fleet, beholder nations, mind flayers, and neogi slavers without breaking Planescape, where the standard form of Outer Planar travel is walking through portals in the City of Doors and the gate towns in the Outlands, and the major factions are either Sigil's Factions or the alignment hosts of angels/devils/demons/etc.
The fact that people are pointing you to 4e material on the Astral Sea is the best evidence of this; it's as if you asked for advice on mashing up Forgotten Realms and Eberron, and were directed to Nentir Vale because it had both Bane and warforged.