I'm just wondering 
2 scenarios :
1)Let's say ur mum's name is the co-owner together with your name.Both you and your mum still got the lifetime exemption. When u sell the propoerty and you want to use the lifetime exemption. So, IRB will take away BOTH you and your mum's lifetime exemption, right. So they is two chances waste instead of one.

2) Joint-name. But you already utilised your lifetime exemption, only left your mum's chance. Then, how will IRB consider this case ? Exemtpion under mum's name still valid but your name is still be taxable ? lol

You need to hard sell on this one. I am slightly believing the the bubble specialists. I have not much courage.