Save a scene file onto an SD card. Load the SD card into your computer and edit the file with notepad. Look for the line that says something like Frame Rate and change the last digit number of that line to a number from 1-35.
The example should look something like...
XXXXX N : Frame Rate ; some random info here
You would change the N... dont touch the X's. This is all from memory.
Save the change you made with the file and load it into the camera. Dont alter the settings or else the frame rate will auto change to 60. I dont remember exactly what N number = what frame rate, but it was something like...