delaying return of cell phone by a month or so.

Last fall I received a call from the local Videotron outlet stating they had some really great fall savings for me.  My last payment had been made on their lease agreement and so I went in and signed up and got a fairly good deal.  The Canada USA package at the advertised price and two pixel 10s for $10.00 each.  Ok, not a bad deal, but two weeks later they were $0.00 as they always are in December.  I need two of them, so that's $20.00 per month, plus taxes, times 24.  So my question for now is how can I stretch my contract an additional month to be able to take advantage of the zero dollar phones? Thanks for your help. Bruce.