having participant-specific image stimuli

I want to construct an image rating task where each participant will see slightly different images. Each participant will be asked to rate 20 images, and half will be the same across all participants, and the other half will be unique for each participant.
Is there a way to do this in DirectRt/MediaLab (I have both), short of manually changing the image files in the stimuli folder between each participant, or creating as many conditions in MediaLab as there will be participants and having a different completely different image rating task in each condition?
I was thinking maybe creating a separate folder with images for each participant, with each folder titled by the participant number, and then using images from the folder that corresponds to the participant's subject number...is this possible?
Otherwise, are there any other options?
Thank you.
Marina