Is there a true plug-n-play setup for a 5.7 with FI yet?

You can get a cable throttle body by BBK through Summit for $350-450 depending on size you want.

http://www.summitracing.com/parts/bbk-1791/overview/
http://www.summitracing.com/parts/bbk-1782/overview/
http://www.summitracing.com/parts/bbk-1781/overview/