Can't use side inputs with Combine.PerKeyWithHotKeyFanout

PerKeyWithHotKeyFanout doesn't allow a user to specify a side input and access it in the CombineFn. When the function `withHotKeyFanout` is called, any sideinputs stored in the Combine.PerKey are dropped. (https://github.com/apache/beam/blob/master/sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/Combine.java#L1571): 

    public PerKeyWithHotKeyFanout<K, InputT, OutputT> withHotKeyFanout(
        SerializableFunction<? super K, Integer> hotKeyFanout) {
      return new PerKeyWithHotKeyFanout<>(fn, fnDisplayData, hotKeyFanout);
    }

We would like to be able to use side inputs and hot key fanout.