It takes zero effort to let a rat defrost in the fridge, unless someone in your home is actively asking you not to, which in that case, water thawing or even just buying a mini fridge solely for this purpose would be great.
Remember, we as humans have decided to kidnap this species from its rightful place in the wilderness for the sake of our own entertainment and profit. The LEAST we could do is feed them with the same care and consideration that we do for ourselves. Yea it can be a pain in the butt, but it's a pain we've all signed up for.