Write a trio wherein each voice explores its own rhythmic pedal. (A rhythmic pedal occurs when a rhythmic motive is applied to any given pitch content. An ostinato implies a more literal repetition in both intervallic and rhythmic elements.)
The rhythmic pedals should contradict the meter you choose.
As a twist, you could have the two lower voices be canons by augmentation on the top voice. (For instance, the second voice can be double augmentation, the third triple augmentation.) A free codetta could end the piece.