I'm not sure if I understood the question right but:

- Use more complex and non-linear levels instead of big, easy ones; Portal 1 and 2 are good examples (I hope you know what I mean)
- Use physics objects which the player can carry around for example to keep buttons activated, etc.
- Use some time-limits
- Use colors; for example: there are colored "energy-barriers" which the player only can pass if he has the same color

...just to name a few ideas I would use.