You don't really "need" any kind of bandwidth, the faster the upstream, the faster the download. Tivo itself can't upload faster than around 700-800 anyway.

When I tested this on a 256 upstream it took around 3 hours to transfer one 30 minute show, I now have an upstream 3 times faster and still need to test it.

If you are handy, you could setup a VPN to the house and bypass having to open those ports. Just VPN and then download locally. Another option is to have someone at home save the content and put it on an FTP server on the home PC with some weird port assignment the ISP won't look for...