Here is an update: They are working on it. I received this via e-mail this afternoon:
I apologize for the delay in my response to your request. I have finally received some information in regards to the External Hard Drive for the DISH 411 model receiver. The receiver’s software has been designed to accept the External Hard Drive, but for some reason our system does not want to add it to accounts at this time. I was not given a timeframe for this to be fixed.
Unfortunately, we do not have a large number of DISH 411 model receivers out in the field, and this may be the reason for the oversight. The proper people have been made aware and are working on this