Well, if the boxes are connected to either the internet or phone at all times, it should not be a problem. I can see Dish saying "NO" if ALL boxes are NOT connected to internet or phone. Years ago when I had 6 boxes in the 2000's, the ONLY way Dish allowed be to have all 6 was so that ALL the boxes were connected to the phone line, and all the boxes dutifully called each month, without fail, but, of course, they still audited me years later, but just the ONE time because the boxes were calling.
Frankly, it is easier and less costly to just have someone use the DA app on a FireTV connected to a big screen. I do NOT advocate that for unauthorized users of the DA app to the account it is connected, but for our discussion, it is a less costly version of account stacking that has none of the safeguards of an exotic install with ALL boxes connected to the internet or phone line.