referencing several cells in a worksheet header

I need to be able to link several cells to create a header. I have a code started, but what i need is this format as the header for sheet1:
First line: Sheet2!b5 (Sheet2!b3)
Second line: Sheet2!b4, Sheet2!b2

Sub UpdateHeader()
   ActiveSheet.PageSetup.Centerheader = Worksheets(Sheet!2).Range("B5").Value
End Sub

I can't figure out how to get the other 3 cells to work in the code.