[NTG-context] Single page in landscape?

I'm sure this is a FAQ, but I can't find an answer which works. I have a document in portrait mode (A4), with one wide diagram - a Gantt chart, created with the gantt-tikz module, and which I'd like on a landscape page of its own. What's the easiest way to do this? I can do it by simply putting the chart on a page of its own and rotating it, but this is a bit of an ad-hoc solution. Thanks, Alasdair