恐怕这种情况没有直接的支持。不过，您可以通过 flatMap 通过为单个输入元素发出多个结果来执行函数。
例如

stream.flatMap(new FlatMapFunction<Object, Tuple2<Object, Object>>() {
    @Override
    public void flatMap(Object value, Collector<Tuple2<Object, Object>> out) throws Exception {
        out.collect(Tuple2.of(/*key1*/, value));
        out.collect(Tuple2.of(/*key2*/, value));
        out.collect(Tuple2.of(/*key3*/, value));
    }
}).partitionCustom(new Partitioner<Object>() {
    @Override
    public int partition(Object key, int numPartitions) {
        return /* desired partition */
    }
}, 0);