You can’t have dynamic attributes, but you may be able to fake it using a list of simple entities that have a key and value attribute that you populate. I’m not sure that is very practical though.
If the number of attributes are fixed, you could create a larger entity that can hold the different attributes. To populate this you could create a fake JSON entity with all the possible attributes set, and define an input mapping based on this.
Another approach if you know which attribute triggers which response is to create a different series of import mappings that you can use depending on the data you are expecting for that attribute.
Hope this helps.