A new function PrintDialog.SetTray allows you to select the paper tray by name.
The only problem is that the tray name is printed specific. To learn what your tray is, you can use PrintDialog.GetTray to see what tray was used in the last printer dialog. This way you can see if your trays are named Tray1/Tray2 or maybe Upper/Lower.
Please try with new prerelease (or email me for a test copy).
This is currently only for Mac and requires to use PrintDialog.Enable and PrintDialog.Install.