Calculating the constants of a permanent-magnet DC motor
All those measurements are to be done with a locked rotor, i.e. \$\omega=0\$, so there is no BEMF involved. But you could try to express the torque constant as voltage constant:
Source Wiki
$${\displaystyle K_{\text{T}}={\frac {\tau }{I_{\text{a}}}}={\frac {60}{2\pi K_{\text{v(RPM)}}}}={\frac {1}{K_{\text{v(SI)}}}}}$$