Level Streaming: best way to fake loading time of sublevels (for testing)?

For a project I use a bunch of streamed sublevels and switch between them. To better test the transition between these levels I’d like to add some fake loading time, for example by adding assets to the level. Since it’s a test environment I don’t want to add thousands of assets to the project just to increase the loading time of the sublevels.

Is there an easy way to fake the load? If not, what type of assets would you recommend? I know this is normally not what you want, decreased performance.