[NTG-context] selectively turn off captions

Hello, I'm making progress in using modes - thanks again for the help so far that was given in the "switching to Context" thread. I have followed Thomas Schmitz' practex article and have set up modes for presentation and manuscript. I am using external figures on most of the slides. In presentation mode there is no need for figure captions (the slide heading and my waffling will suffice). In manuscript mode I'd like to have captions to the figures. I know I can disable captions with {none} for each individual figure, but can I do this _just_ for the presentation? I have looked up \setupcaptions but there does not seem to be a "none" option that could be used for this purpose. Thanks, Roger