What is a hyperlink, really? Its a text "button" that, when clicked, brings you to a website or opens a link of some sort. So in this case, use a button in a tab on the Excel ribbon that when clicked brings you to a website. Easy:
Private Sub MyRibbonButton_Click(Byval sender as Object, Byval e as EventArgs) Handles MyRibbonButton.Click
System.Diagnostics.Process.Start("my website url")
End Sub
Does it look like a button? Of course, but essentially it's just a hyperlink, right?