Being a technical lead on an agile project is a big job.  We've made some recommendations about how to do it in our Tech Lead Checklist.  You should provide some training and practice before you throw someone into the job.  Or, maybe you are the technical lead and you aspire to the ultimate fantasy - a vacation.  You need to train a deputy.  This is the scenario that caused one of our most intense project teams to develop the "release captain" role.

A release captain is simply a person who takes the tech lead role for one iteration.  The established tech lead takes on some individual technical problem, and the release captain takes on overall responsibility for the ticket list, questions about assignments, and reviewing code.  It's simple, it provides the right level of challenge and the right level of support, and it might double your team's tech lead capacity.