Build new usable lookup for Custom Properties

I have established some Custom Properties for my projects (for Test Cases precisely) and would like to update the Excel spreadsheet to be able to import the from xls. I know this can be done by input the property ID, however it is not quite usable. I would like to create my own lookup inside the spreadsheet, in the style of other existing (for instance 'Importance').

Assuming I will have cust prop 'Difficulty' with values Hard, Moderate, Easy, I would like to have lookup list with these descriptive values, which would then be exported using correct IDs - may configure that in you Excel template?