We have landed on using a modified UX Design Sprint format where the Design Sprint is scheduled over the course of 4 weeks, one, one hour meeting a week. Using this method, we are better able to get leaders/stakeholders to make themselves available and it gives us the time to design during the week, conduct user testing, have sidebar meetings along the way if a leader/stakeholder hasn't been available.
We have engaged stakeholders presenting strategy/business problem at the beginning of the sprint and other participants in the sprint are typically made up of UX, Stakeholder, Systems Analyst and CMS, Sometimes we add a Business Analyst. At the end of 4 weeks, we hold a "UX Tollgate" meeting where we invite a larger group and review the designs from start to finish.
Any leaders who haven't been able to participate in weekly design sprints will usually make time to participate in the UX Tollgate meeting as there is a shared understanding that designs will be officially documented to be handed off to the Agile Teams next. It works well for us.