It sounds like you want to have have two plots, one time-domain plot that you interact with using the data cursor, and one x-y plot that gets updated based on where the data cursor is currently located.
I haven't personally tried it, but you could possibly create a custom UpdateFcn callback when calling "datacursormode", pass it the handles to the x-y plot that you need, and have that update the x-y plot based on the currently clicked position. It would also be defining what the data tip would look like, but that's not the main focus here.
-Cam
