It turns out the way to do it is to remove any end caps and locknuts and washers and nuts and then bang the end of the axle really hard against a piece of wood. You will probably make dents in the piece of wood.
This works because cartridge bearings are pressure fit both to the hub and to the axle. (This is really neat!) Both the hub and the axle are stepped to hold the cartridge in place. A hard enough bang will simultaneously make the step on the upmost side of the axle pop the upmost cartridge from the hub and make the step on the downmost side of the hub pop the downmost cartridge from the axle. You can then pull the axle out and remove the other cartridge by poking through a screwdriver or similar and tapping with a mallet.