I've found that I have to wait for somebody to reach a level up naturally. Then, I use the following steps:
1.) Save the game.
2.) Exit to main menu.
3.) Load the game I just saved.
4.) Select the character to level up, then use whichever options I want.
5.) Try to level up and see if the extra points are available.
6.) If I want more points, it is possible to exit the level up process before it is complete. Then you can use the extra options again.
7.) Finally, save the game again (for reasons of paranoia).
What would be useful is an extra set of options to take away surplus power-up points.