Depending how much a team may want your son you might be surprised how much the team will be willing to give up in the "scholarship" negotiations.
Remember that a very low percentage of the players negotiating the "scholarship" portion of the contract actually use it. (I have seen figures in the 4% range) Because of this I think many ML teams look at the scholarship program as an inexpensive add on to help get the deal done.
Another thing to consider is what level of college scholarship commitment the player has? I would imagine the higher the scholarship the bigger the bargaining chip you have. In our case we factored the total estimated four year COA at the school he had his NLI with then added 20% for inflation. While it took months to negotiate the bonus, the school part lasted about 20 minutes.