Not sure what year/model you have, but looking in my owners manual for "flat tire" brought me to the correct area.
I have an 05 OBXT, so all info I'm providing is only relevant to that model as far as I know.
Page 9-4 of the manual
"Note - If your vehicle is an AWD type with an automatic transmission but is neither a turbo model nor a 3.0L model, deactivate its all wheel drive ...."
Basically it says you have to plug a fuse into the appropriate spot and the AWD warning light should come on, this means you are in FWD mode.
To find the fuse box, page 11-68 in the manual. The fuse you want, along with spares and a puller, are in the main fuse box. It's inside the engine compartment, right hand side (as you look in) just above the battery and below the strut mount.
To find the fuse, page 12-8 in the manual. The fuse box is shaped like a rectangle with a triangle attached to the bottom pointing down to the 4 o'clock position. When you open the fuse box look in the tip of the triangle, you should three rectangular boxes, nestled inside those boxes should be an open fuse socket. Plug that socket and your vehicle is in FWD, remember to check that the AWD warning light has lit up inside the compartment.
Hope that helps, I learned a bit looking it up atleast. :P
On a side note, why do turbo and 3.0L not need to put the vehicle into FWD mode when driving on a spare?