Hi,
There's no wheelchair accessible lines to my knowledge but you could check with the folks at
http://ourworld.compuserve.com/homepages/Eshzk/home.htm to confirm this.
My concern would be that you typically need to hike up in the woods to get elevation to go down. The hiking up typically is a rough trail with many steps and some incline. The most difficult time is just hiking up to the lines and then the easy part is going down.
Whatever you decide to do in Costa Rica you'll have a great time. Its a beautiful country and friendly people.