Can I use my friend's PlayStation Plus account to get discounts on my account?

If you have a PlayStation Plus account, you can get additional discounts on games.

I've been using my friend's PSN account to play online. I would like to buy the game under my account, but my account doesn't have PlayStation Plus. Is there a way to use my friends PlayStation Plus discount benefit on my account?

You can not get the discount, BUT if he sets that specific console as his primary console, then all accounts on that playstation get to play online and play all his downloaded games. If you let your friend buy the game, you can play it as well with your own account, just like you can play online on your account without psplus (provided he sets the console as primary).