What's the secret to skating in slip ons and not murdering my feet?
If you mean vans slip-ons, it depends if they are the "pro" version or not.. If they are the regular version your are gonna have to rip out the insole and replace it with something better. Bit of shoe goo (for suede) or super glue (for canvas) will go a long way. And in the end, its a thin piece of fabric either way.. if you get an unfortunate blow to the top or side of the foot, you're fucked.
I would say that most slip-ons have a shorter life span than other shoes.. maybe two or three weeks until they feel like actual slippers.
But I will say that when you're feelin' it, and skating a pair of slips, it's like you're one with the board. They are the ultimate board-feel type shoe, for better and for worse.