It won't work. The cable modems have unique id numbers to prevent folk from just plugging them in. Let's not duplicate that old discussion?
Why not solve this the usual way with routers and such gear?
Ok so I have done a little bit of googling and from what I have read, it seems that it is not possible to do this without paying for another bill. But I am just wondering, if I wanted to set up a wireless router upstairs in my house with 1 cable modem there, and the use another cable modem downstairs for another computer, is it possible to just plug both in or will the cable company charge me double the monthly fee? I have also heard that for $5 dollars extra a month, I can get another ip from the cable company so if I do that will this work?