Peter's on the right track, I think. If you allow hyphenation at all here, then it's going to be funky - I hate Proximity hyphenation.
You might need to share your file to get a perfect answer for this one. When I typeset your example, simply applying No Break to "Plessis" gets the result you want. If I had to, I might use a zero-width space somewhere (I love those things) but it doesn't seem necessary here.