What I've found to be very helpful is to insert a quick upstroke with the wrist after the little note:
Practice that slowly and mechanically with the left hand only, doing the upstroke itself as fast as possible regardless of the tempo. The unaccented notes should be 1-3" high, and the accented notes 6-10+". As you increase the tempo into performance range, you can streamline the motion so it feels more natural and swinging, but if you keep thinking of that upstroke with the wrist before the 2 and 4, it the entire groove will feel much more relaxed, and your 2 and 4 will sit right on the money— or wherever you choose to play it. You'll also be able to play it at softer (and probably louder) volumes than with the “jerk” stroke.
A rudiment I've found helpful with shuffles in general is the right handed flamacue:
If you put it in a triplet rhythm, with the first flam landing before the beat, you have the kernel of the shuffle in the left hand:
Once that's comfortable, you can do the flamacues so the repetitions overlap. Here your left hand will be playing the shuffle rhythm (though with the accent on 1 and 3 in this case), and your right will be playing quarter note triplets:
The quarter note triplet in the right hand is actually helpful in cross-checking your rhythm, and can also give your shuffle some place to go when improvising— more about that later.