At this late date, given potential for complication, I would advise against us. Many have reported that they were able to have their 622 activated, but in doing so, the work order for antenna installation was closed resulting in an additional headache of rescheduling the installation and once again getting the date for installation moved out.
I was in the same situation as you are right now. Received my leased 622 from Dish last Thursday, but my installation was scheduled for Friday. Instead of waiting idly, I unboxed the unit, then hooked it up so the firmware was downloaded prior to the installation. I was also able to program remote codes and get to the setup menu to scan for and save my local OTA stations.
Once done with that, I reconnected my existing receiver so that I could go back to my normal viewing.
Once the installer came, all he had to do was mount, aim, peak, and plug a cable into my switch.
Having been an early (ahem $1,000) adopter of the 921, I can say that the wait for the 622 was worth it!
Good luck!
Spence