Yes, but only when using bga-workbench.
I think there are two methods:
1) Lightweight Method
That means using the modules-directory (as mentioned by RicardoRix and Draasill)
2) Using bga-workbench
Which requires alot more configuration, but I think the (initial) effort is worth it, especially if you want to try some fancy phpunit/tdd coding
The method uses a different approach to include your classes, it compiles all of them into the uploaded game.php
(Which to be honest can make debugging more cumbersome, because the line numbers in exceptions will refer to the compiled file)