I think if you set the tivo to 720x576 resolution and your stb to 16:9 (pillarbox 4:3) then it should be ok. However there will be no signal to tell your widescreen tv to switch to widescreen mode.

If your stb supports 4:3 pillarbox (black bars on the left and right) then the above should work. Just leave your widescreen tv set to 16:9 all the time.

ZollyMonsta
(no widescreen telly myself..)