Can I make a bottle up like this?

[Icanonlytry]

Would it be ok to make a formula feed up by adding 5 scoops of powder to 2oz of boiling water, shaking well then adding 3oz of cooled boiled water which has been kept in a steralized bottle? Ds is having top ups after his breast feeds but not after every feed so making a bottle up before his breast feed means throwing it away if he is satisfied from the breast feed but if he has to wait until i have made and cooled a bottle he gets himself into a right state.
I know the powder has to be added to boiling water to steralise it but does the amount of water make a difference?
Typing one handed on my mobile so sorry for any mistakes.

that should be fine, otherwise what about just using cartons? if it's top ups you may well be able to do without them soon. also 5oz as a top up seems like a lot of milk. most breastfed babies will only drink 24oz/24hr so if feeding 3hrly should be approx 3oz bottle, 6hrly 6oz etc so as a top up 5oz would be a big volume

I'm not sure how much hot water you'd need to sterilise the amount of powder - there's no guideline on this. Could you not make the bottle up and then plunge it into a bowl of ice water to cool it? Or could you put him back on the first breast again while you wait for it to cool? You can keep swapping back and forth between sides several times per feed.

Thanks for the replies, I cant find any guidelines on how much water is needed either, sure I read this method on here somewhere but cant find it now..
Ihave been making the bottle before i start feeding him and leave it to cool whilst I am feeding him but feel I am wasting alot of milk by doing this and it is so expensive..
Have tried using the premade cartons but they dont seem to agree with ds, he gets very uncomfortable with tummy pain and was being sick after even a small amount.
Was hoping ds wouldnt need the top ups for long but although he doesnt always need it he needs it a few times a day.
5 oz does sound alot and he doesnt always take it all, sometimes only takes 1~2oz but sometimes he will take 5. He does take both breasts atleast once during a feed but then he starts fussing and wont latch on again.