  In this paper we present two methods to evaluate non-factorizable corrections
to pair-production of unstable particles. The methods are illustrated in detail
for W-pair-mediated four-fermion production. The results are valid a few widths
above threshold, but not at threshold. One method uses the decomposition of
$n$-point scalar functions for virtual and real photons, and can therefore be
generalized to more complicated final states than four fermions. The other
technique is an elaboration on a method known from the literature and serves as
a useful check. Applications to other processes than W-pair production are
briefly mentioned.
