If you play the extensions, you should adhere to them. Here's what my approach would be:
Create some introductory tension by pedalling B natural (in whatever syncopated rhythm you choose) through the whole progression once. Second time through, go up a tritone to F natural (see how that sounds over the E-7). If you play the F high enough, it should work. A high E pedal would work over the third and fourth chords as an alternative.
Then go up again to a higher B natural for the third time, and finally a high F natural for the fourth time. Over the fourth F Natural, play down the scale F E D C B into your walking groove.
For the bulk of the tune, consider that B-7(b5) is essentially the same chord as the G7, except that you can play a C natural over the B-7(b5) but you shouldn't over the G7. For bars one and two, work out some things with the notes B D and F and for bars three and four, work with the notes E F B and C. Try to create two similarly-structured lines from those two note groupings.
Tuning a mellotron doesn't. - Robert Fripp