Yes it's possible but you have to know what you are doing.
If you use Apache as web server you should backup the .htaccess file in your website root, then open it and find the clearly market W3 TC sections (look for comments).
Find where it lists jpgs, pngs etc and add those 2 files at the end of that list. Save the .htaccess and you are done.
If you are using Nginx you have to open the nginx.conf file in the root of your website, find the list with many file extensions separated by | and add those 2 file extensions. The important list is the first, that should look like:
location ~ \.(asf|asx|wax|wmv|wmx|avi|bmp|class|divx|doc|docx|eot|exe|gif|gz|gzi
p|ico|jpg|jpeg|jpe|json|mdb|mid|midi|mov|qt|mp3|m4a|mp4|m4v|mpeg|mpg|mpe|mpp|otf
|odb|odc|odf|odg|odp|ods|odt|ogg|pdf|png|pot|pps|ppt|pptx|ra|ram|svg|svgz|swf|ta
r|tif|tiff|ttf|ttc|wav|wma|wri|xla|xls|xlsx|xlt|xlw|zip)$ {you may also add them to the second, even if it's only used in case of files not found.