It is not allowed do to Dish's business rules but I do know that some people have been able to work around this. You would have to find a very helpful Dish agent to make this happen.
I'd be interested to know how they did this. I consider myself a pretty helpful "Dish agent", and I have tried, out of curiosity, to see if I could get it to work. Tried to reactivate a 311 on a customer's account who had just switched to the Hopper. Purchased 311. I had to let them know, no, it would not allow me to do so.
I can't say it can't be done, just that I've not had any luck getting it to work.
As a Dish employee, my opinions are my own, and do not represent Dish in any way, shape, or form.