Automatic character import + build

Hi, I want to create automatic system that would build UFE game (practically training room project with custom stage) but with different characters. Idea is that user would supply my system with just a model and then scripts would build a game with it. I know that you can build unity game with script/from console and it works.
Alternative option is to add characters to already existing game build. But I guess that model needs to go to your editor first.

Is there any way to add player models with minimum human involvement with pro version? I guess that upgrading to source code version would allow me to rewrite some things here and there and make system that I need, but I don’t know how much work would it be…

Hope you can help;)