I might have some fundamental misunderstanding, because I don't understand how this could be.

> stepping out until the probe has gone enough distance to be sampling a separate bit of surface.

Why not have a probe already at that distance, so it's gathering something of that surface?

My assumption here (knowing very little of gravitational lensing) is that the gravitational lens still has the concept of an "image surface", where a translation in that image surfaces can be mapped to some translation in the projection of the thing being viewed. Are you saying that if I put two probes up, with some appropriate spacing between, they can't collect different stripes of the same surface, at the same time?

But if the probes are recording continuously and sending it all back, you can probably identify points that are simultaneous on two tracks, after the fact.

But that gives you just a scattering of points on that day. The next pixel over, for each probe, will be for a different planetary day. Your image, stitched together from all the lines returned by all the probes, is an image smeared over at least as many days as pixels in each line.