Huh. I can honestly say I have never heard this one, myth or not.
Seems feasible, but one would have to assume that the Japanese would have the forethought to consider their rifles to be battlefield pick ups.
Which means they would have had to conclude their troops were dead (or captured).
Which means they would have had to conclude they were at least losing ground.
If they did that, that is some sneaky tactics right there. There was no talk about that sh*t in Art of War.