Sure I'll share if I found the solution ;-)
The code I used to draw the bone lines is pretty similar to the code in the Corona runtime.
In Javascript, it's like this:
for(var j=0, m=this.bones.length; j<m; ++j) {
if(this.bones[j].boneData.length > 0) {
context.save();
context.strokeStyle = "red";
context.translate(this.bones[j].worldX, this.bones[j].worldY);
context.rotate(-this.bones[j].worldRotation * (Math.PI/180));
context.beginPath();
context.moveTo(0, 0);
context.lineTo(this.bones[j].boneData.length, 0);
context.closePath();
context.stroke();
context.restore();
}
context.fillStyle = "green";
context.arc(this.bones[j].worldX, this.bones[j].worldY, 3, 0, Math.PI*2, true);
context.closePath();
context.fill();
}
}