-TH, without really analysing the chords and a transcription of his solo, I can't, at the moment, tell you exactly what he's doing, but it sounds to me like, in the beginning, he's playing a parallel chord progression in another key, based on an extension of the basic chord/key construction.
For example, a CMaj7 chord can be extended with a D(9th), F#(#11), A(13th). If you look at that chord another way, you can think of it as D major over C major. If you extended a chord progression in the same way, you could be playing in D major over the chord structure in C major, giving a bi-tonal quality to the solo line. So, take a chord progression and transpose it to a parallel key and play an improvisation on that against the original chord structure. Of course, an interesting improviser is going to mix it up and, without going through Osby's complete solo, I would suspect that's what he's doing.
If you want to learn how to do this, you can use parallel keys, like I mentioned, or tritone relationships, etc. A book that illustrates coming in and out of keys on standard progressions is Bunky Green's "Inside/Outside" which you might find interesting.