A programmatic way to dismiss the Welcome Back panel is to put this code in your Normal.dotm file:
Sub AutoOpen()
Selection.EndKey Unit:=wdStory, Extend:=wdMove
Selection.HomeKey Unit:=wdStory, Extend:=wdMove
End Sub
This code moves the cursor to the bottom of the document and then back up to the top.
If you’d rather not fiddle with VBA macros, then I’ve also put this capability into an Add-In. You can configure the add-in to dismiss the Welcome Back panel, and also to force documents to open in Draft View mode (or any other view of your choice); which restores functionality that MS removed in Word 2013. The add-in can be downloaded from:
http://rath.ca/Misc/VBA/Word/ViewMgr_v2.1.zip