Export to Excel template

This can be done but I don't know if it can be built into an IDEAScript.

To do it manually you would need to have your Excel Template with the field names you have input into row 1 open. You would also need to make sure that the IDEA file fields were arranged in the same order as the Excel columns.

IDEA does give you the ability to copy and paste data from IDEA to Excel using the CTRL+C, CTRL+V keyboard shortcuts.

In your scenario, you would highlight your entire IDEA file by left clicking on the blank square above the number one and to the left of your first IDEA field name (upper left corner of the data window). This will highlight the entire IDEA file. Now CTRL+C to copy all this information. When you do this in IDEA the field names are not copied, just the data.

Now go to column 1 row 2 of your Excel template and CTRL+V to paste all the data.

You can also use a script but the easiest way is what Steve is suggesting.  If this is something that is reoccuring then you might look at scripting it.

Consider exporting the data from Idea to Excel as per normal , then use a macro in Excel to format the headings as required. This should be a very light weight task . 
Alternatively , export to from Idean to Excel as per normal , then use the resultant Excel file as a "datastore" and have a 2nd Excel file "import/link" data from the 1st Excel file .  ie use the output from Idea as a staging area