I really wouldn't recommend that either. I seem to recall Bell having something in one of their terms of service about 90 days and new receivers. Not sure if that's time to activate, time they must be left activated, or what.
You are trying to do the somewhat honourable thing, when at the end of the day Shaw wants your business, and part of the intent with this promotion is to take away your ability to just switch back to Bell.
Also, not sure who told you that to get 2 receivers you have to do it online. When I did it I just called the main Shaw number and said "I got this thing in the mail.........." If you want the phone number that's on my flyer PM me.
Just buy 2 used receivers and be done with it. Don't waste your money and risk Bell getting upity by getting better receivers that Shaw won't care about anyways.