I have found a way to solve this for the LaserJet 400 M451dw and Windows 8.1.
Changing the settings under Print>Preferences from within a program does not seem to work. Instead open:
Devices and Printers > Select the Laserjet 400 > Right Click > Select Printing Preferences. Change the Paper Size from A4 to Letter > Click Apply on the bottom right of the form. Now when you print using the default settings, it will pass Tray 1 and print on Tray 2 as it should.
I also created two Printing Shortcuts. Both use Paper size = Letter, Paper Source = Tray 2, Paper Type = Intermediate (or the setting you want), and then one says Print on both sides = Yes, the other Print on both sides = No.
Hope this works for others too!