  In this letter we extend the factorization procedure of the deep-inelastic
hadron tensor, proposed by Qiu, to include non-zero quark masses. The manifest
gauge invariance of both soft and hard parts is preserved. Using a so-called
spurion to generate the quark-mass terms, the simple parton-model
interpretation is also kept. The calculation of the deep-inelastic
transverse-spin structure function $g_2$ is used to illustrate the algorithm.
