  This paper presents first results on the line profile shapes from a
circumstellar envelope in bulk motion as modified by a microlensing event. Only
geometrically and optically thin spherical shells in uniform expansion or
rotation are considered here so as to emphasise the information content
available in the profile shapes. In particular it is demonstrated that for the
case of expansion, the line emission can increase by significant factors and
the time variation of the profile shape is symmetric about line centre. For
uniform rotation the line emission also increases significantly, but the time
evolution of the profile shape is distinctly asymmetric. Thus, microlensing is
seen to yield information about the velocity field in the extended envelope. We
elaborate on (a) the observational advantages of tailoring microlensing
programs toward detecting extended circumstellar envelopes, (b) the use of
multiline observations to infer other properties of the envelopes, such as the
ionization stratification, (c) the use of the continuum excess emission at
infrared wavelengths as a means of probing the envelope structure, and (d) the
use of polarisation for constraining the properties of ``clumpy'' winds.
