Mixing build.sbt with project/Build.scala and aggregates

Before I had something like this (simplified), using sbt 0.11.3:

// project/Build.scala
import sbt._
import Keys._

object MyBuild extends Build {
   lazy val standardSettings = Defaults.defaultSettings ++ Seq(
      version      := "0.2",
      scalaVersion := "2.9.2"
   )

   lazy val main = Project(
      id        = "main",
      base      = file( "." ),
      settings  = standardSettings,
      aggregate = Seq( sub )
   )

   lazy val sub = Project(
      id        = "main-sub",
      base      = file( "sub" ),
      settings  = standardSettings
   )
}

But I want to keep as much information as possible in the plain build.sbt file. So now I have

// build.sbt
version      := "0.2"

scalaVersion := "2.9.2"

And

// project/Build.scala
import sbt._
import Keys._

object MyBuild extends Build {
   lazy val main = Project(
      id        = "main",
      base      = file( "." ),
      aggregate = Seq( sub )
   )

   lazy val sub = Project(
      id        = "main-sub",
      base      = file( "sub" )
   )
}

But that doesn't seem to mix in my settings from build.sbt into the sub projects:

> show version
[info] main-sub/*:version
[info]  0.1-SNAPSHOT
[info] main/*:version
[info]  0.2
> show scala-version
[info] main-sub/*:scala-version
[info]  2.9.1
[info] main/*:scala-version
[info]  2.9.2

How to remedy this? I also tried to add explicit settings to the sub-project, e.g.

• settings = Defaults.defaultSettings
• settings = Project.defaultSettings
• settings = MyBuild.settings
• settings = main.settings (sure this one should do?!)

...but none worked.