You need to use the Excel Wizard when openning the spreadsheet. It will allow you to not read in the headers. All you need to do, is to go to
File==>Open
then navigate to the Excel file you want to read in
Single click on the file you want to read in, and then click on the down arrow next to the Open, and select Excel Wizard. It will walk you through the options on how to read in your Excel File.
Once you have read in one file, you can right click on the "Source" green triangle in the Table Panel in the upper left corner of the JMP Data table. If you select Edit, you will see the JSL that you can use to read in the Excel Files
Jim