Conversely I find that a good way to differentiate a mentalist is to limit the powers. Limit mind control to just having the target feel extremes of some emotion. Limit telepathy to requiring eye contact. Or use a non-mental special effect, like ultrasonics, pheromones, or magic.
Mechanically mentalists can easily justify the use of creative non-mental powers. Drains and Suppress are really useful; Suppress INT is cheap and can be AoE and still effective, and cumulative Drain EGO is perfect for setting up a Mind Control. One thing I've always wanted to try was using something like Duplication to simulate a speedster-mentalist, whose speed of thought vastly outstrips his physical body. And you could use a mentalist to buff other party members too--consider giving a teammate an adrenaline rush, suppressing his ability to feel pain, or helping him focus on a target.