No you cant extend the date of anything in this process.SO he has to land before the date they give him,if he has to do things in his home country he still has to land then go back.You have to understand it from their point of view.You did this process to get into Canada as a permanent resident,and they are giving you this chance,if you blow the chance then thats your choice you will have to do the process again.
The only way you can ever get an extension on the timeline where you land is tell them you cant land on that date,then they will tell you to redo your medical and they will base the visa on that one,but thats up to the IO if he or she even wants to.And of course it will cause a delay as they have to send you forms for the medical you will have to pay the costs again.
And if it expires on October 1st then they are asking for the passport to put the visa in and he will have to land before Oct 1st no exceptions.