Oh my gosh - I have to try this. It could be life changing!!!
That's so funny, that's exactly how I've been making my cappuccinos for the past couple years. I was just lazy and didn't want to have to clean the steamer regularly so I played around with this technique, except I shake the milk in its container then pour into a mug to heat in the microwave.
Kristine, it never occurred to me to try this, but I'm happy to have discovered it!