  We investigate the cross-section for the production of a low-mass
colour-singlet cluster in $e^+e^-$ annihilation with a large rapidity gap
between the colour-singlet cluster and the other jets. It is argued that such
events are the cross-channel analogue of large-rapidity-gap events in
deep-inelastic scattering, and therefore could in principle be used to
investigate the analytic continuation of the BFKL pomeron to the positive-$t$
kinematic regime, where one would expect the trajectory to pass through
glueball states. The cross section can be calculated in perturbative QCD, so
that the infrared scale arising from non-perturbative effects, which prevents
an exponential fall-off with rapidity gap in the case of deep-inelastic
scattering, is absent in $e^+ e^-$ annihilation. Correspondingly, the cross
section for such events decreases rapidly with increasing rapidity gap.
