That should be calculable. Orbital mechanics, orbital period, and minimum determinable arc of JWST. Though another thought is that doppler might also reveal v

That should be calculable. Orbital mechanics, orbital period, and minimum determinable arc of JWST. Though another thought is that doppler might also reveal velocity, if a spectrum could be obtained. Since the system is nearly perpendicular to the Solar System (we're viewing it face-on rather than from the side), those shifts will be small.