We have explored the circumstellar effects on the Li abundance determination in a complete sample of O-rich Galactic asymptotic giant branch (AGB) stars, previously studied with hydrostatic models. We use a modified version of the spectral synthesis code Turbospectrum and more realistic extended model atmospheres that consider the presence of a gaseous circumstellar envelope and a radial wind in these massive AGB stars. The Li abundances are determined from the 6708 Å Li I resonance line. The Li pseudo-dynamical abundances obtained are practically identical to those derived with hydrostatic models (a maximum difference of 0.3 dex is found in the only super Li-rich AGB star in our sample). The low Li abundance and therefore negligible Li I column-density in the circumstellar envelope likely explains the small differences between extended and hydrostatic models. Our results confirm the activation of the hot bottom burning (HBB) process in massive Galactic AGB stars.