Rotarycraft is the most reliable way to do it.
Failing that, there's a little-known bug left over in vanilla MC that lets you do it.
You need a wooden pick (although I hear you can do it with your bare hands too, never confirmed that bit though) and a lot of patience. You need to set yourself up DIRECTLY below the block, not move at all and attack the underside constantly for a set number of swings.
This causes a stack overflow in java and temporarily causes the block's hardness value to wrap around negative. It's only momentary but it's long enough for another swing of your pick to break the block.
I can't quite recall the exact number of activations you need but it takes between 45 minutes and an hour iirc.