Exporting data into a running spreadsheet

Our company has instituted a new policy forcing us to use a form for every purchase, and keep a control log that contains the same information on the form.

I've created my form and played around with the various exporting to excel features but I'm not getting what I need.

When I export to excel using the "merge datafiles into spreadsheet" it DOES export the data to the file, but it overwrites the data that was there previously.  I need to KEEP the data in the excel file and ADD to it each time I create a new form, so that I have a running list of all purchase forms created.

It would be nice if I didn't have to SAVE the form each time, then reopen it and do the export, if there was a button on the form I could click that would just auto export all data into the spreadsheet, not overwriting again, but adding to it.

Is this even possible?

Any help is appreciated.

Thank you,

Matthew