Transitioning 1yr old to sippy but still have frozen milk

bloopblopp

Hi! Looking for some advice. My little guy turned 1 a few weeks ago and I had an oversupply early on so I still have a LOT of frozen breastmilk but we went to the pediatrician and she no longer wants him using bottles. She said sippy cups from now on only. For the last few months he's taken 3-6oz bottles warmed up at daycare but with this transition I'm feeling overwhelmed. I would still very much like my LO to consume the frozen breastmilk but I'm worried he won't take it from a sippy, especially if it's cold. I have never heard of anyone serving a sippy warm. He love love loves drinking water from a sippy but when I've offered milk a few times it's been hit or miss. Any advice is appreciated!