  Background: Extensions of single-reference (SR) energy-density-functionals
(EDFs) to multi-reference (MR) applications involve using the generalized Wick
theorem (GWT), which leads to singular energy kernels that cannot be properly
integrated to restore symmetries, unless the EDFs are generated by true
interactions.
  Purpose: We propose a new method to regularize the MR EDFs, which is based on
using auxiliary quantities obtained by multiplying the kernels with appropriate
powers of overlaps.
  Methods: Regularized matrix elements of two-body interactions are obtained by
integrating the auxiliary quantities and then solving simple linear equations.
  Results: We implement the new regularization method within the
self-consistent Skyrme-Hartree-Fock approach and we perform a
proof-of-principle angular-momentum projection (AMP) of states in odd-odd
nucleus 26Al. We show that for EDFs generated by true interactions, our
regularization method gives results identical to those obtained within the
standard AMP procedure. We also show that for EDFs that do not correspond to
true interactions, it gives stable and converging results that are different
than unstable and non-converging standard AMP values.
  Conclusions: The new regularization method proposed in this work may provide
us with a relatively inexpensive and efficient tool to generalize SR EDFs to MR
applications, thus allowing for symmetry restoration and configuration mixing
performed for typical nuclear EDFs, which most often do not correspond to true
interactions.
