Hm. This is definitely possible through MediaLab. There's a few ways you could go about completing the task.
1. Custom items allow for HTML to be used within your MediaLab experiment. By utilizing the power of a custom item, you could use the HTML ability to easily create scrolling marquee.
2. Program a small tool that does the same task, and can be loaded at the start of the experiment.

Option 1 will not allow for a continuous scroll through multiple experiment items; whereas option 2 will.

Programming a small tool like this may be a bit daunting; however if you could provide me with your completed experiment, the text required to be scrolling through, and an in-depth explanation of when you want the text to be displayed, how big you want it, where you want it to be on screen, and how long you want it to be displayed for, I would gladly consider taking the time to write a tool up for you that you could use alongside with your experiment.