I just did the rear wheel bearings on the RH rear axle, earlier this week and had the same problem. The only thing that works is a longer bar to get the leverage. I tried a 48" breaker bar and could only get it to ~.25. Finally, I pulled the handle off of my Arcan floor jack and was able to get it within tolerances. The other tricky part is keeping the bar from slipping every time you applied torque.
When I decide to take on the LH side, I may find some real heavy flat stock that I can drill holes in and make a holding fixture that will permit slipping a floor jack handle over the end, or even clamping with heavy u-bolts. Something very similar to what is used in this video:
Setting pinion bearing preload on the Ford 8.8" axle - YouTube