It's possible, but I don't think the tools to accomplish this are yet in the "public domain". Almost certainly the 2TB drive no longer has the capability to add an external drive on a "plug and play" basis, as that has always been the case for a Tivo with a (non factory)upgraded internal drive. Only stock, factory Tivo units/drives can be upgraded via plug and play.
There are 2 TB + 2 TB set ups offered by weaknees.com(and maybe others), but the means to do so are "in house". I think this would also be the case for 2 TB internal + any other external.
There are 2 TB + 2 TB set ups offered by weaknees.com(and maybe others), but the means to do so are "in house". I think this would also be the case for 2 TB internal + any other external.