You must have mutual agreement between the supervisors and the staff members involved that cross training is a good idea. The benefits must run both ways. Mentors must feel they are getting something out of it. The person mentored must feel that it's worth the time and effort. Top management and supervisors must be generous with words of support for participants and the cross training program.
Timing is everything.
You must have a system to sustain the cross training and reap the maximum benefits from it. That means developing self-teaching audiotapes, videotapes, manuals and guidebooks. You must keep it voluntary as much as possible.