This is a script that will import a series of excel files and add a virtual field. The script first asks for the folder in which the excel files are located and then it asks for the name of the worksheet. The worksheet and format must be the same for each excel file. Line 116 of the script hold the eqn for the virtual field, it will need to be changed based on the needs of the script.
Joost, you will have to play with line 116 to get it to work for you. I don't have access to different language versions of IDEA so I can't test out if the formatting is correct.