Is it possible to inherit default_service inside the scope?

[realGWM]

I want to implement the following behavior:
If there's no binding for some path in /a/** invoke some_a_default, if there's no binding for any other path (/**) invoke some_global_default.
I've tried the following:

App::new()
    .service(
        web::scope("a")
            .service(
                web::scope("b")...
            )
            .default_service(web::get().to(some_a_default)),
    )
    .default_service(web::get().to(some_global_default))

This works as expected in cases like /non_existent (calling some_global_default) and /a/non_existing (calling some_a_default), but in case of /a/b/non_existent it calls some_global_default, while my intention (due to it being inside the a scope) was for some_a_default to get called.
It is possible somehow for everything inside the a scope to "inherit" the default_service?
If no, what would be the best solution for this? I see only two options, which are not perfect IMHO:

1. Manually add default_service to every scope inside a scope.
2. In some_global_default check if request path is starting with /a and handle it differently.