It sounds like you have a good start at addressing the issue, actually. There is really no shortcut to dealing with the palm key notes.
If you were practicing a tricky passage in a written-out piece, I would suggest starting very slowly and working your way up to tempo. I would also suggest working on evenness by practicing in "rhythms." What I mean by that is, say you are practicing this passage:

Being careful to be especially strict with the rhythm, you would practice in both of these ways:

If you don't trust your time to be exactly precise, use a metronome. Also, no swinging here. The rhythms need to be strict.
Once you are somewhat comfortable with those rhythms, try these:

Again, the rhythms need to be strict. The purpose of these rhythms is to encourage evenness by practicing the transitions between notes in real time, but not all at once. That is difficult to understand until you have done the exercises for a while.
The rhythm exercise is good for evenness everywhere, not just in the palm keys. As for the palm keys themselves, try to avoid extraneous motions.
Finally, since you say you are working on improvisation rather than written-out passages, try writing your own exercises. I took the one you started with, but you will want to come up with other passages to try. Do not neglect the high F♯ either, provided that you have the key. (It is, of course, possible to play F♯ without a high F♯ key, but that is a separate topic having nothing to do with palm keys.)