My solution for a similar setting:
I use the seal function as a second signature set instead. Delete all the seals and copy all the images from the signature folder into the seals folder.
In the certificate.php-file for your types you might have to change the dimensions of the print_seal-command to those that are used for the print_signature-command.
In the language file I changed the strings for signature into "left signature" and for seals into "right signature".
In my company both signature sets are the same. Of course it is possible to have two separate or overlaping groups of signatures (e.g. your bosses on the left and you and your fellow teachers on the right).