The TransitionControl doesn't support this scenario out-of-the-box. What you will need to do is to load the image, before settings it to the TransitionControl. We don't have such an example, but we will consider creating one, because it sounds like a common scenario. I logged this in PITS.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items.