There's no way to automatically do it, but you can create different buy-in profiles and use one for early buy-ins and one for late buy-ins. In fact, once the tournament starts you can change the "default" profile, and that way any buy-ins that happen after tournament start will automatically use the "late" profile (you won't have to change the profile each time you buy-in a player after the tournament starts). It's not automatic, but as close as you can get. This way, you only have to make 1 manual change when the tournament starts. Let me know if you need specific instructions.