Employer permission agreement to do contract programming work in spare time

I'm in discussions with a programmer to do contract work for my startup. He works full time programming at a Massachusetts company whose business is unrelated to mine and my project would be done in the programmer's spare time on his own equipment.

I have an agreement prepared that includes wording assigning the copyright and that programmer warrants no outside conflicts. However I feel it would be safer to have it in writing from his employer that he has permission to do the outside project.

Do you have any comments on taking this approach? How can I get a sample employer permission agreement to allow outside contract work? One that also releases claim to IP ownership to the work and that wouldn't require providing a lot of details about the project to the employer.

Do you know how Massachusetts labor code is regarding IP ownership by employers?

I can only answer the most general of your questions:

Do you have any comments on taking this approach

If I'm working at a company, do they have intellectual property rights to the stuff I do in my spare time? Second, the comment you ask for: It is very wise to understand the mechanical factors (e.g. his contract with his employer) that might affect your ownership of the work your contractor does. But if you're really scrappy you may also want to consider the social factors (e.g. his relationship with his employer), which might make those mechanical factors either very important, or irrelevant.

I am not a lawyer, this is not legal advice.