I am afraid you have to map it to a tabular excel before you can import it.
Adding to Jacobs answer: Yes, the current ExcelImporter only works with each row having the same type of data based on the column information. (for e.g.: Name Age as columns, each row is a persona name with his/her age)
What you need is a custom java action.
Read the excel file using file uploader. Then parse this FileDocument using Java POI libraries (may be there are other libraries as well) and when the data is read you can create new entries your Entities and commit them.
See one example here