I found my answer so will share it.
In FEMAP under the Model/Output submenu note the Fill command.
Assuming you want to calculate the Triaxiality Factor for load step 10 use the Fill command to fill vector 30000 in load step 10 as follows:
(VEC(10;60016;!i)+VEC(10;60017;!i)+VEC(10;60018;!i))/MAX(1;VEC(10;60030;!i))
where:
60016 thru 60018 refer to the principal stress vectors
60030 refers to vonMises stress vector.
The MAX(x,y) function prevents division by zero errors. I haven't figured out a good value to replace the 1 with yet.
When displaying this vector set the contour display to have an upper limit of 2 and a lower limit of something like -2.