Large projects lead to adaptations. Often, teams and/or stories need to be subdivided into pieces that are a better size for XP.
Planning meetings with the customer before the first release planning meeting save time and gives you a chance to educate the customer and set expectations.
If the customer isn't onsite, team members need to schedule regular meetings with her in addition to ad hoc meetings and contact with individual stakeholders.
Different stakeholders have different priorities. Work with them individually and together to get them to speak with one voice.
Educate the customer to improve his skill at writing acceptance tests.
Additional documentation, such as a formal test plan, may be necessary in larger projects or where the customer requires a test plan.
Large projects whose teams are in different locations can successfully plan and complete iterations by sharing responsibility for task breakdown and estimation and by remote pair programming.