How to give relative rotation to armor stand?

I'm trying to make a armor stand spin around in 1 degree intervals in a Repeat command block on 15w47c. The problem is, '~' doesn't seem to work for relative rotation when using with the Rotation tag in /entitydata.

Here's what I've tried;

/entitydata @e[type=ArmorStand,r=10] {Rotation:[~1f,0f]} 

and

/entitydata @e[type=ArmorStand,r=10] {Pose:{Head:[0f,~1f,0f]}}

Both just move to 1f, instead of increasing every iteration. I just need the head to turn, but the whole armor stand is fine too. Any suggestions?