Transition level while switching server in multiplayer

Basically, I want to use something similar to seamless-travel when switching servers. As defined in the documentation, seamless-travel is not possible when I have not visited the server before.
Also I know that level load operations can only be done in the main thread. Therefor it blocks e.g. playing in a small level while the real level is loading.
Do you know any workarounds for this?