I would be able to give you Tampa ideas a lot better but have always thought it would be cool to cycle in the WDW area.
The first thing I want to point out is be careful. Many of the people driving in the area are tourists who are busy looking for streets or looking at the scenery and not looking for cyclists.
I would jump on Google Earth or Bing maps and try to plot out some routes. Here is what I would try to do:
Start over by the Grand Cypress Golf course. You may be able to park there or over by Mystic Circle.
Take Winter Garden Vineland Rd. south/southeast to Vista Blvd.
Vista will head south and then slowly turn west, stay on that past North Bonnet Creek Rd.
You be passing Lake Buena Vista Golf course on the left and Eagle Pines on the right. If you stay on Vista you will then also pass Osprey Ridge and you will be in pretty much a tunnel of trees.
Continue straight and you will pass the Fort Wilderness entrance.
Vista will loop a little to the right and then pass under the monorail that goes from MK to Epcot. Just after you go under the track you will take a right onto N. World Dr. This is the less busy road when compared to World Drive and is probably safer.
Stay on N. World past the turn off for Ft. Wilderness and head past the Contemporary (You'll go under the water at this point and through a tunnel).
You will go past the MK and behind Space Mountain. This will bring you back to where a lot of the facilities buildings are.
From there I would just explore the roads. You can then either head back to where you started or they can go back to one of the MK resorts and you can meet them with the car and bike rack at one of the hotels. They could also go back to whatever resort you are staying at.
Depending on where exactly you start over by the golf course the route is about 6 miles from there to the back of MK. There are a lot of roads back there to explore so you can make it a pretty long ride if you tour around the backstage area and then head back to the start.
