How create osgi manifest for bundle built in task?

Question

I have to create osgi manifest for bundle created by task that uses proguard. For osgi part I'm using sbtosgi plugin (ver 0.6) Currently I tried something like this:

  object BuilderKeys {
    val pkg = TaskKey[File]("package")
    val bld = TaskKey[File]("build")
    val targetFile = TaskKey[File]("targetFile")
    ... 
  } 

  lazy val settings = ... + BuilderSettings.default(bundle) + BuilderSettings.osgi(bundle)

  object BuilderSettings {
    def default(configuration: Configuration) // initializes bld (task that creates one uber-jar using proguard)   

    def osgi(configuration: Configuration) = inConfig(configuration)(SbtOsgi.defaultOsgiSettings ++ Seq(
      fullClasspath in Compile := Seq(Attributed.blank((targetFile in configuration).value)),
      pkg <<= (OsgiKeys.bundle dependsOn bld) map { f: File =>
        f
      }
   ))          
  }

Running bundle:package creates jar with manifest but not based on jar created by proguard. Is it possible to force it in some way?