Don't forget you can increase the A/P pitch authority by using the speed brake. You only need to crack it for the increased authority.
Boomerang, crack the speed brake and select a slower speed, say 300 initially, then use speed brake as required. The increased pitch authority will do the rest.... Maybe.. And if it doesn't who cares.
A320 tested Vd is 380 kts and M0.86. Accept the Overspeed. She won't fall apart.