If your printer accepts PCL commands, you may be able to use a PRINT field.
A PRINT field is simply a type of field that allows you to send instructions
directly to the printer.

There are 3 possible data values for duplex setting:  PRINT 27"&l0S" simplex
PRINT 27"&l1S" vertical duplex . PRINT 27"&l2S"  horizontal duplex
(bookformat)

The codes after PRINT are 27 (escape), double quote, ampersand, lowercase L,
0, 1 or 2, uppercase S and finally terminated with a double quote.

Thus for horizontal duplex you would insert the following field :
{ PRINT 27"&l2S" }