Thanks Georg and Alejandro for your responses. It seems that a script is the way to go, but I ended up doing something simmilar to what Alejandro suggested: opened each image, created the necessary previews, modidified the file names in the process container, and applied the container.
It is a lot of work. Wouldn't it be nice if the ProcessContainer built from History would carry previews setting data (similar to masks, dynamic crop, etc), and "variableize" the file names?
best
Ignacio