From what I've tried so far, it seems the best way to prevent the nip slip is constraining the fabric at the apex of the bust, which fortuitously coincides with the location of that naughty anatomical detail that we're trying to hide. I'm also not pinning the dress to the shoulders in this particular render but may have to for other poses. In order to prevent the crumpling issues that we had in the Bookworm pinafore, I'll have to make the dress load with a bit of separation from the skin. Here I simulated that by simply scaling it to 102% at frame 1. 

-- I'm not mad at you, just Westphalian.