I would just pick up a Slingbox and be done with it. Easy to use, high quality and no hassle. VPN will be challenging to get working and video quality may suffer if you do get it working. Slingbox fixes these issues, although it does piggy back off live viewing, overall it will be a better solution. You can also stream onDemand and anything else your TiVo can play with no restrictions.
TiVo XL4 (2TB) HDMI/MoCa
TiVo Roamio Plus (3TB) HDMI/ETHERNET/MoCa & Slingbox 350
(4) - TiVo Mini (MoCa) HDMI, two on each TiVo
DirecTV HR22 HDMI/ETHERNET & Slingbox Solo