If you're going to use the term imitation breast milk, why not just go with imitation breast instead of "bottle"? It might be accurate, but it's still offensive.
Offering Neighbor Baby the Gift of My Milk - Page 6
This made me think of the term "artificial nipples" which I know what is meant-- pacifiers and bottle nipples-- but for some reason it makes me think of rubber nipples being put on over human nipples and it makes me giggle every time. Or of the bottles that are intended to be breast and nipple shaped. Those give me an inward giggle as well. (No offense meant to anyone who uses or used them, it just strikes me juvenilely funny.)