I found the solution. Here's the subroutine for processing the click event of
the Lotus Notes action button.

Sub Click(Source As Button)
Dim xlApp As Variant
Dim xlWkb As Variant

Set xlApp = GetObject("", "Excel.Application")
Set xlWkb = xlApp.Workbooks(1)

With xlWkb.Sheets(1)
..Range("J3").FormulaR1C1 = "Customer Name Here"
..Range("J4").FormulaR1C1 = "Customer Address Here"
End With
End Sub

I knew it would be something easy.