Multiple optimal solutions

Hello,

        I am solving an optimization problem with ECLiPSe where
        there are multiple optimal solutions, i.e. different
        assignments of values to the variables that lead to the
        same optimal value of the objective function.

        I would like to retrieve all these optimal assignments
        but, as the minimization predicates are not resatisfiable,
        this cannot be done simply through backtracking (I think...).
        Is there another way to find all these solutions?

        By the way, could this same idea be implemented to find
        all the assignments that lead to the second (and, in general,
        i-th) best value of the objective function?

        Thank you very much in advance.

Best regards,
Tallys