It's just personal choice, however using it as a lever in the fashion described WILL damage both poly and cedar. It is possible to lever against the top bar of the next frame, near the sidebars but even this can cause damage to the frame.
Next time you use the J tool, use it horizontally and not vertically. Fit the J end between top bars, rotate a little and it's free. This is possibly even easier than the standard tool, especially if you are suffering with wrist pain as I am.
Next time you use the J tool, use it horizontally and not vertically. Fit the J end between top bars, rotate a little and it's free. This is possibly even easier than the standard tool, especially if you are suffering with wrist pain as I am.