I would still use the seige engine for resolution. Pick how many skills you want each player to have (X). Tell each player to pick out X skills when they create their character. Treat those skills as favored class skills (i.e. add your level to the roll). You could either use the skills list from 3.5 (or whatever edition) or just have the characters make up their own skills. I'd disallow skills that mimiced another class ability, with perhaps a few exceptions (maybe the barbarian can climb like a rogue). Not a lot of precise character developement, but I'll just run 3.5 for that.