2 steps to this:1) Add the measures you need before the vocals come in with the measure tool, as follows:
Select measure tool, click on a measure before which you want to add measures, select "Insert" from the "Measure" menu, then type in the number of measures you want.
2) Once you've created your piano introduction, then, in Page View, select the Page Format tool. Under the "Page Layout" menu, select "Optimize Staff Systems." Select your options and click okay.
Optimizing will make invisible staves in systems with no information in any of each staff's measures.
