  Generating a spin vortex in a $^{87}$Rb dipolar spinor Bose-Einstein
condensate in a controllable way is still experimentally challenging. We
propose an experimentally easy and tunable way to produce spin vortex by
varying the potential barrier height and the width of an additionally applied
optical plug. A topological phase transition occurs from the trivial single
mode approximation phase to the optical-plug-assisted-vortex one, as the
barrier height increases and the width lies in an appropriate range. The
optical plug causes radial density variation thus the spin vortex is favored by
significantly lowering the intrinsic magnetic dipolar energy. A type of
coreless spin vortex, different from the conventional polar core vortex, is
predicted by our numerical results. Our proposal removes a major obstacle to
investigate the topological phase transition in a $^{87}$Rb dipolar spinor BEC.
