Yes, but there are some caveats:

limited to 1 or 2 Terabytes (I forget) and HAS to be a single platter drive. AND self powered- not USB bus powered.

It's also a SLOOOOW process. I recommend "sending to External HD" only 3-4 shows at a time. If you try more than that, they sometimes bog down.
It does work though, I've "saved" way too many cartoons for my daughter, and a few select shows that I wanted.

I recommend doing it occasionally anyway for long term keeper shows as HDs fail all the time in consumer devices (especially ones that they {sat/cable providers} can give out for free by the millions...)