Creative thinkers, I need your help!

A friend of mine very generously donated her frozen milk stash to me, knowing that I am having supply problems and have to supplement my 7 month old with formula.

The problem is that, in order to save a little money, my friend stored her milk in cheap sandwich bags. The milk froze fine in them...but whenever I put them in hot water to defrost, tiny holes appear and the milk leaks out everywhere!

How can I save this milk? I've thought about peeling the bag back from the milk when it's still frozen and then putting the frozen milk inside a cup which I would then put inside a bowl of hot water...but the problem there is that the plastic is so thin, you can't peel it away from the frozen block of milk without leaving behind tiny pieces of plastic.

The only thing I've been able to figure out so far is to partially heat it in a bowl of water, and as soon as I see the milk start to leak out (when it's about halfway frozen), take it out quickly and try to empty it into a milk bottle, taking out the little frozen chunks by hand and plopping them in too and putting the bottle under hot water for the remainder.

I'm still losing some milk this way, and it's driving me nuts. Any other ideas on how to save this milk?