You need moar lanes!!!!
Anyway, you need two slots to run both cards in and you can't just have two joyful cards leeching off of one slot which is 90 degrees WHICH is also hanging off the side of your board.
actually you might be able to, it'd just split into 2x8 I think, but they'd be single slot, and the bottom one would be toasty and all very unstable. i agree not a great idea.