Enslave Val, and put her in Bimbo personality.
Periodically as you are levelling her and yourself up to Level 14, Mrs. Rack will have conversations. In the first one, lie to her.
In the second one, use the flirt spell, and then use boost on her after picking an option of which part of her body to try and pleasure. In the second to last one, offer to fix Mrs. Rack (DO NOT ENSLAVE HER, ENSLAVING HER WILL HARD END THE ROUTE). Then after fixing her, go back to your room, put Val back into Bimbo personality, and then return to Mrs. Rack. This will set you onto the NG+ triggering scene for the Bimbo World route.
There is then a subplot in the Bimbo World NG+ called Bimbos Gone Wild, which requires you to repeat the process done in NG, but at the point where Val is about to bimbofy Rack for you for the first time, try to intervene. That will then start Bimbos Gone Wild, which has you going around town starting in the streets outside your house and seeing Val slowly bimbofy everyone, when she does Molly in the shop make sure to go back in after the scene and chat with Molly, before heading towards the school, and to follow Molly's advice she gives in that talk with her after the scene where Val bimbos her.