Both WIPO and NAF have a form for requesting a joint suspension of the proceeding. When the registrar is notified of the joint suspension, then both parties inform the registrar that a settlement pursuant to transfer of the domain name has been reached, and have the registrar transfer the domain name. Transfers from the respondent to the complainant are permitted.
Alternatively, have the complainant withdraw the complaint, and then proceed with the transfer. Some complainants will be suspicious that you won't follow through, so they usually prefer going the suspension route.
By the way, if the dispute is at WIPO, the complainant will receive a $1,000 refund in fees paid for the proceeding, if it is settled prior to going to a panel, which is something to think about...