you would have to drill and tap the spleen it's self then screw in the nipple then it would be out of balance so you might want to put another nipple on the opposite side to get the grease where it should go, assuming there is enough room between the spleen and swing arm tube, then an access hole in the swing arm say 12mm diameter to line up with the nipple in the spleen and a plastic bung to cover the 12mm hole
Pete... the spline is inside the female coupling. To get grease inside that coupling, onto the spline teeth, nipple(s) would need to be fitted into the coupling.
But that coupling runs very close to the inner walls of the swingarm tube..... no room for nipples between it, and the tube.
And I dunno whether I'd fancy putting a 12mm hole in my swingarm tube...... dunno...?????
Anyways.... if ya wheel's off for a tyre, it's prolly only an extra 15 min job to pull the diff and grease the splines while you're there....