It's actually fairly easy to acquire and track fast movers. I was a serving Air Defence soldier for 14 years, qualified GDF-005, ADATS, Skyguard and Javelin missile system. Using passive radar we could pick up an aircraft, and then manually track it easily or autotrack if needed. Even if the AC is, say 450-500 kts, at a distance the AC really doesn't seem that fast. Even with the GDF without radar handoff, the electric drives, cross wind sensor and lead angle computation enable us to track AC visually, and fire electrically (present number of seconds = number of rounds) or manually (foot pedal = fire until autoloaders take over).
In regards to the BMP 3, it can elevate it's barrell to 60 degrees, of course being on a reverse slope will make it even more. It also has a ballistic computer, cross wind sensor, stab system and laser ranger..I (IMHO) believe it is very possible. I'm not sure the max slant angle for the 30mm, but put enough lead up there, something's bound to hit it eventually.