Yes this is possible.
Download the whatsapp apk to a pc then use apktool to reverse engineer the app (unpack apk, change package name in AndroidManifest.xml to something like whatsapp2, repack, resign).
when you are done install and you will now have two whatsapp's pick the second one and install. This should allow you to configure the second line, however be sure that one version is installed to your phone and the other version is installed to your sd card (different locations are crucial otherwise there will be conflicts)