Although I've never had to use Neocate with DS1, I have read a great many success stories on these threads. Also, as a breastfeeding supporter, I have listened to many mums telling me how they worry that their babies will not take bottles/sippy cups before they return to work.
Does your baby accept bottles or cups of 100% breastmilk? I am wondering if it is the taste of the Neocate or the feeding method that is the problem.
I have a DS2 who is the same age as your baby, and he totally refuses to take even 100% expressed breastmilk, so it's clearly not the taste which is the problem with him. In your position, I'd be inclined to start offering just breastmilk in a sippy cup or bottle before you even start to think about introducing traces of formula. That way, you can get your baby used to the alternative feeding method. However, as I said, I have no personal experience of introducing Neocate!
Some mums find that their babies are more likely to accept expressed breastmilk or formula from their partners or friends. (If you are the one offering your DS a cup or bottle, he is more likely to refuse it, because babies are clever little things, and of course they know when their mum's breasts are only a few tempting inches away!)
Babies get most of their nutrition from breastmilk or formula until they are at least 12 months old but, depending on how your baby eats, you may even find that you don't need to give much alternative milk during the day (especially if he is being given Neocate Spoon in food). Some babies go for long periods during the day without milk, then make up for it during the night. (However, if you are working full time, you might struggle with night time feeds unless you are happy to co-sleep so that you can continue to get some rest while breastfeeding.)
What sort of childcare have you got organised? A busy nursery is more likely to require that your baby fits the established pattern of standard meals and bottles, but a childminder or nanny could be more flexible.
Good luck with this. Returning to work can be hard enough without the added worry you are facing.