I have always thought that JSF should add a business-converter for such issues. So we should have a way to convert between the model type that we need for the renderer, and the model-type that the backing-beans use.
You could register such a converter on the input-component like the normal converter, businessConverter="...". We could also cover stuff like the joda-date with this.
Eventually, we could even add a central registry for this in MyFaces where you can register business-converters centrally and hence let the renderer automatically retrieve such a a converter for the backing-bean datatype and the datatype it needs.
We'll explore this idea here