Cloning modems

[PumaTechTV]

I have been on comcast cable for a while (I have subbed modem) but there is one problem. I live in 2 different places, and In the house that I use the least is the one that has the internet. My most used house has no internet, so I usually have to go to starbucks every time I need to use the internet. I have tried cloning my modem by putting the mac address and serial # of my old modem (A) to my new modem (B) but it did not work. I was wondering, how do I clone my sb5100 from my other house (house A) to my new spare sb5100 that I'm going to keep in my other house {house B} (the one with no internet).

Modem Info-
My new modem ( Motorola SB5100 ) has SIGMA X2 (A)
My subbed modem ( Motorola SB5100 ) is not modded (B)

UPDATE: I live in california