$100K vs. $200/hr I guess that's how you get to 39.5%...

3.8% surtax is real, you will have to pay.  so the difference would be more than 5%. 

If your son is making 30K, his bracket would be 15% at most, which means his CGT is 0%.   It is a big difference and I think you are well advised to talk to an accountant.