Child Tax dependent

My boyfriend is divorced with 2 children. The Child Support Order Says that if he is current and up to date at the end of the year with his payments that he may claim his son. Well, the IRS now requires that his EX sign form 8332, Realease of Claim to Exemption for child by Custodial Parent. This is in addition to his court Order. She refuses to sign. We have been through 2 Attorneys and cannot find any advice on how to MAKE her sign. Please help.