A great structure is having an internal champion present on each team, unit, office, etc. that can easily provide answers to benefit questions. This structure is particularly important if the company is spread across several locations without HR on the ground in each locale.

On the more proactive side, having the champions provide information through rotating monthly topics in presentation, newsletter, or dropping into team meetings can be extremely effective. For example, a champion might put together a January newsletter for employees that will be utilizing parental leave detailing the process and what they need to know ahead of time.

Training of champions can take place through HR or existing champions that know company policies, engagement can occur through project management and implementation, and empowerment through the respect and gratitude earned. Internal champions are often looked to for management positions following effective leadership and project execution.

1- Sit previously used employees and ask their opinion and tell them to develop a plan.. For instance... "you guys used it, how can we make others also use it"
2- Tie them up with an incentive goals to signup more employees / group champions to work together
3- Arrange informative training sessions in your company, raise awareness, ask for enrollments
4- If benefit is a third party contractor; Get more "juice" from contractor and tell your internal champions they will have more benefits if they sign up more.

I remember once we wanted to increase the foot traffic to one of our restaurants. We gave 25% discount to our employees to come and try, didn't get much traffic. We than offered a "refer 3 full table / get free dinner up to 4 people" than we increased our bookings and spread the name of the venue. I guess it really depends on your benefit, if it is an internal benefit or an outside contractor benefit that pays commission to your business i.e. insurance policy...

Easy... set up demonstrations of these amazing benefits. Call your vendors that you use and create a Presentation that all can see what it is you offer. Make sure you put this presentation into a synopsis for interviewing candidates so that they too can see what you have to offer.