Hi Luc, you say that currently Vizard already outputs on the two projectors, correct?
This probably means that you are using a dual VGA/DVI output graphics card and are using horizontal span mode for outputting on the two 'screens'.
If this is the case, then probably all you need to to is to change the 'field of view' of the rendered output, so it outputs a larger field of view, possible also with a different horizontal/vertial ratio.
The command to do so is
viz.fov(50, 1.333) , see
http://www.worldviz.com/vizhelp/VizHelp.htm#viz/fov.htm
for details. Changing the 50 to a higher number and adjusting the aspect ratio should do the job for your setup.