You can create a second data connection to your lookup table and use "data blending" to do what you want. Search the online help or knowledgebase for "data blending".
I have two tables one is Enum and other is Data as you said Enum is a lookup table having numeric code and description where as data is having only numeric value.
you have to set up a left outer join to achieve the result.
I have attached sample data file (.xlsxa) and .twbx as well.
Hope it will help you out.