trait MyWrapperBound {
  val message: String
}

def wrap[T <: MyWrapperBound](message: String): T

def wrap[T <: MyWrapperBound](message: String)(implicit factory: String => T): T

case class SimpleBound(message: String) extends MyWrapperBound

object SimpleBound {
  implicit def factory(message: String): SimpleBound = SimpleBound(message)
}

def wrap[T <: MyWrapperBound](message: String)(implicit factory: String => T): T = macro ...