Or just drop all your seeds (click once and press r, best to do this in your house) and they should stack on the ground together, then you can pick them up as one lot :)
I agree though it would be great if they went into the existing stack when you examined one.
I typically examine all my plops on the ground (at home), and let them autostack that way (sort of like Sunburst does--didn't know about the "r" thing, I'll have to experiment), but it's still time-consuming, especially if the piggy doesn't stay in the same general area.