Yes! loadPixels() totally did the trick! Thank you!
I must have totally overlooked that line in the example sketches... but of course now that I look for it, there it is.
For the benefit of the clueless (ahem), maybe the documentation could be augmented to make it clear that Capture is an extension of PImage? I see that at least one other person was confused by this: https://forum.processing.org/topic/updatepixels-method-for-capture-object
-Cassidy