Starting off with one stave, then double stave of selected instrument(marimba)

Hello, I am composing for marimba in an ensemble context. The marimba is used for the first measure then there is a large number of measures in which it rests. The first measure is a two note chord on a single stave, but when it re-enters into the ensemble context it needs to be notated on a double stave. How would I do this? Thank you.