Take Guilmant's Morceaue Symphonique, for example:
The top line is from the piece. The second line is the same rhythm without the pitches. I've circled two notes that points of greater musical tension. Aim at these notes.
Once you can play very expressively on a single pitch, add in the pitches and see if it has gotten better.
This reminds me of that observation that, when a person loses one sense (sight, for example) other senses become more keen. Once deprived of convenient pitches, you become more keenly aware of other elements that go into phrasing: dynamics, intensity of sound, vibrato, note shape, etc.
This one-note technique can also be used to clarify rhythm. Here's an example from a Galliard Sonata...
A lesson trick that can work: first the teacher and the student play the rhythm together on one note (not robotically but with good emphases). Then, the teacher stays on the single note while the student plays the passage with the pitches included.
Hope this helps.
