base64 encode image files using a datasource

SoapUI easily lets me right click and "Insert File as Base64", into my web service request, which is great by the way. However, I'm looking for a way to do automated testing essentially using a Directory data source of files that need to be base64 inserted. I've searched everywhere, but can't figure out how to do this. When I use File or Directory datasource, it doesn't base64 encode my files/images.

Myself and a couple coworkers are looking to purchase full licenses of SoapUI, but unless I can figure out how to do this, it won't work for what we need.

Your help would be greatly appreciated. Thank you!