HOW-TO: Di2 Sprint Shifters in a 1x10 application

So I'm thinking about a project bike that the SSCXWC frameset got started in my head.

I also saw Brian Bressler's post on his Asylum build (http://cowbell.cxmagazine.com/forum/topics/asylum-meuse).  This is similar to what I'm thinking.

My big question is- with the Di2 sprint shifters, do I need to have shifters already or can I just plug those into the junction box?  I'd be going for DA or Ultegra 10spd Di2 as I've got the wheels and it will be a bit more "budget" build that way.

There was a shop I used to work at that had a Cannondale with canti's but had the sprint shifters but I forgot to ask how they did it.  

Any insight and knowledge is appreciated!

Thanks