You need to create a Custom Converter to achieve this.

You can refer to this link for a example on how to create a custom converter.

And here you'll find how to use the Custom Converter you have implemented along with the reactive property

Don't forget that you need to keep the instance of the deserialized object in order to really use the Reactive Property. If you deserialize the object every time, you'll override or create a new instance of the properties, losing the observers. This may be useful for it.