The only thing that comes to mind immediately is to print them to a file or otherwise export them from Excel, concatenate the results and then read the output into Monarch. If you output as PRN or PDF of some other file formats you can use Monarch to open the multiple files directly. If you export to a csv type file from Excel you should be able to concatenate the results and read it as a single database file in Monarch.
You could of course open the Excel files in Monarch, export from there to a common output file or Excel worksheet if you will not exceed Excel's record limits, and then read that as a single database.
A batch file or VB code could wrap that into a single process action button.