In my teens I farted on my best friends little brother. Made it natural. He was taking his turn playing a video game and sitting on the floor. I was standing talking to his brother. I leaned back a touch and let it rip on his shoulder.
His reaction was priceless. Horror and "aahhh I felt my shoulder vibrate!"
So if you can enchant a mana stone to hold a spell to maintain the cold then another stone to gather ambient mana to keep it going you can have infinate spell generation and then you've got your foundation all set.