How can he be employed for a job he is not skilled to do!! Are you saying that he is subcontracting his employment?
Can he become a contractor? If so, he can register for income / employer tax and raise a monthly invoice. Employer won't mind as they are avoiding Employers Prsi as well as all those other benefits employees get. However, you will need to consider the loss of these benefits and satisfy Revenue as to the employee v self employed status.