Hi.
My son has been on neocate since he was 3mo (supplementing bf with me on a restricted diet till I cracked at 6mo) and he is 3.5yrs now. He's allergic to dairy, soy,wheat, eggs, seeds, nuts and numerous other things.
He was on the neocate bottle till almost 3yrs. He wouldn't drink it in a sippy cup so was losing required nutrients. Instead of fighting it we just kept the bottle.
I know that sounds like a long time, but one thing a nutritionist told me was that because he has so many issues around food, it is best to keep all behavior and attitudes as mellow as possible. He doesn't need more stress around food and should be comfortable around what he needs.
Part of the story is that he was at a school that didn't use sippy cups and went straight to regular cups from 6mo on. So he was already use to regular cups for water, juice, etc.
We transitioned him more and more to cups of formula during the day, losing the last before-bed bottle around 3yrs. We did the bottle fairy story then too. It is easier to negotiate with them when they are a little older. 20mo is a difficult time no matter what!
I'd try transitioning other drinks to regular cups first, then work on the formula. We still used a sippy cup to shake up the formula, but then mostly take the top off. If he wants the lid on his formula we let him and it makes his formula special and maybe more comforting.
What ever you do, try to keep it low-key. There will be many more challenging food situations to come so best to start from a relaxed place.
Maybe this was a little vague, but hopefully it gives you some ideas.
Happy to share alllergy challenge stories any time if you want.
S.