Yea I could do that, but I've heard that Amazon will charge you their $250 for not keeping the phone on the line you purchased it on for at least 181 days.
I hope not I just did what he is thinking doing 3 days ago.
Bought my son a new subsidized Note 2 on a data limited plan.
Then transferred my unlimited account on the new subsidized phone and then gave him my old GNEX.
I actually went to Verizon and informed them that I intended to swap phones and wanted to make sure my unlimited data plan would be untouched. Manager said it should not be a problem.
Verizon guy activated the new Note 2 on my sons account and then just swapped the sim card and viola I now have the note 2 on my unlimited account (same number) and my son is on my GNEX.
So you should be able to buy the note 2 for your mother in law activate it, then swap sim cards.
Actually you may need to get a 4g SIM card from Verizon if the one from amazon does not have one.
good luck