I will stress that you need a means of mounting the saw if your going to learn how to hand file correctly and quickly. . . . you need a vise be it a big bench vise, a home made one just to hold saws, or a stump vise used out in the woods.
Here is a whole thread with ideas on that:
http://www.arboristsite.com/community/threads/tree-machine-filing-clamps.240030/
Also, a cool, new receiver mounted vise that could work well for this in the field:
http://www.lawlessgroup.com/Wilton-ATV.html
Philbert