Is there a way to handle the last case differently in a Scala for loop?

You may take the addString function of the TraversableOncetrait as an example.

def addString(b: StringBuilder, start: String, sep: String, end: String): StringBuilder = {
  var first = true

  b append start   
  for (x <- self) {
    if (first) {
      b append x
      first = false
    } else {
      b append sep
      b append x
    }
  }
  b append end

  b
}

In your case, the separator is }, { and the end is }