Unfortunately using a setter that converts the value is currently the only way to do this. PrettyFaces supports JSF converters for path and query parameters, but currently only for converters that are registered in faces-config.xml for a specific type. And you will probably don’t want to change the default converter for ALL Booleans as this may cause various issues.
We plan to implement that the user can choose a specific converter for each query/path parameter but this feature is not finished yet. Here is the corresponding ticket: