Do you want its output to also go back to the client that called the first script? That does make a difference.
If the 2 scripts share no variables, where does the second one get its apache environment from? Do you mean that the second script invokes with a separate copy of the environment from the first, or an ENV attained elsewhere?

How about a system call - blocks the calling program until the called program is done.
or an exec() - which will end the current program, and replace it with the new one.

Each solution has different caveats.