The best chance you have to help him is if you become involved in the hiring process. Is your company currently having trouble finding quality workers? Do they they pay through the nose to recruiters for new placements?
If your colleague were to ask for a raise and imply that he'd be willing to leave the company without one (no need to commit to anything in a negotiation), and your company cannot identify the value he is providing then they may be persuaded by considering the cost of replacing him. If you are involved in the hiring process and explain how difficult it is to find quality candidates and how expensive the good ones are then that might help the company see that giving him a raise is the cheapest and lowest risk option.
If your colleague were to ask for a raise and imply that he'd be willing to leave the company without one (no need to commit to anything in a negotiation), and your company cannot identify the value he is providing then they may be persuaded by considering the cost of replacing him. If you are involved in the hiring process and explain how difficult it is to find quality candidates and how expensive the good ones are then that might help the company see that giving him a raise is the cheapest and lowest risk option.