Most of the attractions at WDW have a least some covering for the line, so you should be able to move into a shaded area without a lot of trouble. WDW has a lot more room than
Disneyland has, so they were able to build larger queues with roofs to cover them and many of the lines are inside or well enclosed once you have actually entered the queue.
One that I can think of where the wait is in the sun would be the new Finding Nemo musical show at AK. The theater holds a lot of people and the wait can be up to 45 minutes before. You should be able to wait in a shaded area to the side while the rest of your party is in the line, then join them later.
You can also request a Guest Assistance Card (GAC) to let you wait in a shaded area. But, because most of the lines are shaded, it may not be all that helpful (the stamp actually says a "shaded place to wait when the line is in the sun for a prolonged period of time" - which may mean something different to you than to the Cast Member). There is information about GACs in the disABILITIES FAQs thread near the top of this board.