As long as you are not in a contract you can do so.
There is a $5 surcharge added if you don't have a "base package" though..
I bought my 811 from Sears and paid full price for it since I only wanted Dish's HD package and their CBS-HD feed only and did not want to have to sign a year deal with Dish and receive the 811 at a reduced cost.
From what I keep seeing there are a LOT that are still waiting on theirs. I got mine in a 5 days and did the install myself.