I'd be curious to know how you make it harder, since it's just a matter of feeding them cards it's like many things in the game, with an entry point based on how much money you want to spend.
I got lucky and opened a Diamond in my pre-order packs, sold it and bought 50 packs, got another Diamond. This continued until without spending any real money I had opened more than 400 packs. It was pretty easy to feed my cyborg to 99 at that point.
Of course, I've been achievement chasing, so he rarely plays, but since he can do anything I want him to he's an awesome bench player.