Once I calmed Frank down, he went out to "play" with the plush stuffed dog in the orchard (let's call her Plushy), while I put Vanya in his harness combination, armed myself with treats, and walked out around the barn, perhaps 100 ft from Plushy and Frank. The instant Vanya saw the two of them, he started pulling and vocalizing with excitement and trying to run over to them (he had already greeted Frank, so this wasn't about seeing Frank--it was his classic attempt to greet a new dog or person. Not aggression, but over threshold. Oops).
So we regrouped, retreating back behind a barrier, while I gave Vanya time to calm down so we could try again with a less intense setup (Frank was no longer near Plushy, Vanya and I started further away, and my treats were better).
We then did a series of quick exercises around her, staying at first about 100 feet away while Vanya practiced LAT, hand targets, sit, focus, "this way" (sudden changes of direction), and heel. I'm not really sure if Vanya wants more distance or less distance as a reward, but I know that he always wants salmon as a reward, so he got a lot of crumbled costco salmon burger. He was able to perform his cues, as long as we kept moving and I didn't let him stare at Plushy (he could glance, but then I wanted him to look back at me--not just to avoid going over threshold, but also because I didn't want him to figure out she's fake.) We didn't get all that close, because Vanya was pretty intense about glancing at her and then whipping his head back to me, and I didn't want to send him over threshold. However, he was able to offer calmer signals after several pass-bys at a distance--softer mouth, lower wagging tail, softer posture.
So: until he figures her out to be an imposter, we have a way to practice!