If you're going to Hawaii Water Sports at Koko Marina, that is the same place in Hawaii Kai. Yes, you can wakeboard there but they aren't allowed to weight the boats down per water regulations in that area, and also, they have to run circles which cause a lot of rollers. Finally, because they share that waterway with other water industries like the scuba & parasailing businesses, that also makes the water choppy.
You can try posting a message on www.oahuwaterskiclub.com
(my home club) and see if you can get a pull from one of the members. Most of the club are slalom skiers, the majority of the wakeboard members has declined over the years unfortunately. But you may get lucky. The clubs are located at Keehi Lagoon but you need to be connected with a club member to use the clubhouses. Also, the site is located about a 1/4 mile off shore so you can only access it by boat.
There's also another really active club out there called Na Alii waterski club but I don't think they have a website.
As for the bus, you may be able to carry your board on the bus but I'm not sure. They allow boogie boards so you may get lucky. If you get in touch with anyone at Keehi Lagoon though, you're going to have to find a way to get to the docks because it's a far walk from where the bus would drop you off near Sand Island.
I only come home to visit my family usually in the spring time for a couple of weeks but I'm not sure yet if I'll be coming home this year. I hope it works out for you!