Can you explain what "flagging" lights is, in terms of lighting for stuido photography, and how to do it?

I am working on a photography project in which I have shot Fujia Provia 400 color transparency film (slide film), which will then be projected with a traditional slide projector onto a white seamless background in a studio. I am going to pose a model in front of the seamless so that the projection falls onto her, then shoot the whole image on 35mm, 800 Kodak Portra color negative film. While discussing this in my photography class, my professor expressed concern that there wouldn’t be enough light for a short enough exposure, even though I will be setting up with a tripod and the highest speed film I could get (apparently no one makes 1600 or 3200 anymore, or the photo stores in NYC don’t carry them).

Anyway, I had said I didn’t want to use external lights (if I did, I would only be able to use hot lights; no strobe allowed), because I didn’t want extra lights to wash out the color or strength of the projection, either on the model’s skin (who will be posed far back enough that she will be touching the seamless), or the image on the background. Her solution was “flagging” the lights, a term I’ve never heard, even having worked in a photography studio, and she couldn’t manage to explain what it is, much less how to go about doing it. Do you have any idea of what kind of lighting this is, or how I could set it up using just a small hot light kit? She asked me to google it, and I tried with no success (I searched “flagging lights,” “flagged lighting,” “photography flagging,” “flagging hot lights,” etc., etc. Does this sound familiar to you at all?