There are some ways to practice this. First, you have to understand the underlying motion. It's actually very pianistic and if you are in control of the mechanism (this has nothing to do with fingers) it is not that difficult. I don't mean to demean the difficulty, only to say, it isn't as hard as you think.
Think of this gesture as one of pouring tea from a kettle. To pour tea from a kettle, you have to tilt it enough so the lid pops open, then the liquid will come out. In tilting a tea kettle, your elbow (in the left arm) moves in a clockwise direction. "Tilt the kettle" towards the chords; the octaves will play themselves.
To practice: practice the octaves by themselves until they are melodic, with a strong touch.
Practice the chords by themselves with a light touch until they are rhythmic, meaning they sound like off-beats.
Practice playing the octaves one octave lower than written, and the chords loco.
Practice playing the chords one octave higher than written, and the octaves loco.
Practice playing the octaves one octave lower than written, and the chords one octave higher than written.
Practice playing the octaves as two sixteenths, or two thirty-seconds, instead of one eighth note.
Practice playing the chords as two sixteenths, or two thirty-seconds, instead of one eighth note.
Get the idea? Be creative.
Walter Ramsey