Probabilistic Concurrent Constraint Programming (PCCP) extends concurrent constraint languages by providing probabilistic choice operators. These operators have proved to be useful in implementing randomized algorithms as well as stochastic processes. In this report, we present an instance of PCCP where probabilistic choice operators are modelled with constraint combinators. This modeling allow us to deal with a new kind of problems where the probabilistic choice is only partially known. An implementation under the form of a library of SICStus Prolog is in progress. The major practical application of our work is the statistical structural testing problem in software testing.