Hi,
One way to make the bass sound more melodic is by playing chords.
Tapping can achieve a guitar plucking/piano playing type of sound.
The motion is similar as hammer on.
We will try a G chord for this explanation.
The 4 notes that you are going to tap are G (root) D (5th) G (octave) B (10th).
The fingering is similar as playing bar chord on the guitar.
Now your left hand fore finger on the root, followed by right hand fore finger on 5th , middle on octave and left ring finger on the 10th.
Give it a try :)