I am responding to this old thread in case someone searches and finds this issue looking for a solution.
There is a script called setSpecialSample and it is found in the /opt/XRXnps/bin directory of the FreeFlow Print Server. When you enable the script, it changes the behavior of the sample function from sample every x setsto sample every x sheets. This will enable sampling for VI files.
To enable this feature:
1. Open a terminal window on your FFPS system.
2. become super user by typing "su", pressing enter and entering the appropriate password.
3. enter the following commands at the # prompt:
# cd /opt/XRXnps/bin
# ./setSpecialSample 1
4. Restart the FFPS software
To set the sampling behavior back to its default setting follow the above instructions and replace the 1 with a 0 in the ./setSpecialSample command.