From 1&1's terms & conditions, emphasis mine. I know I wanted to do such a thing with my own web host, but they *all* have such clauses in their T&C. I seriously wouldn't recommend using web hosting as a backup solution as they can pull the plug at any time at their sole discretion since you are in clear violation of their terms.
You shall at all times use Web Site Space exclusively as a conventional Web Site. You shall not use the Web Site Space or Your Services in any way which may result in an excessive load on the 1&1 Equipment, including but not limited to installing or running web proxies, using your allotted space as online backup or storage, or mirroring mass downloads. Use of Web Site Space and Your Services shall be in a manner consistent with this Agreement and shall not in any way impair the functioning or operation of 1&1's Equipment or network. Should your use of the 1&1 Services result in an overly high load on the 1&1 Equipment, in 1&1's sole discretion, 1&1 may suspend your account until the cause of any such overload is determined and resolved.