use a typed expression as a variable.

				
					{
    "id":"_ID_",
    "jsonrpc":"2.0",
    "method":"hub.scenes.expressions.set",
    "params":{
        "name": "maxValueOfSomeParam",
        "params": {},
        "code": "return 2526",
        "valueType": "int",
        "metadata": { "info": "maximum value of parameter" },
        "variable": true
    }
}