Make it as a mod. Then you can put in your own menu screen and the other stuff. You can select before the game starts your mod in the launcher. Thats the best way, and your mod need less space to share. Enigma 2666 for an example needs for the prologue nearly 1 GB of Space, and thats only the music, voice and some stuff. The old models needs also about 700 MB on the HDD. And still needs the prologue.
I think you want for Eagle Rising, a few music samples from WC1, voice for your pilots, a few cutscenes and a lot of WC1+2 models. Thats need some space on the HDD or your Sharehoster. I would make it as a mod.