Try using the force user directive:
force user = root
This would make it so any action on that directory would be as if root were performing the action.
If you give us more information on your problem, there might be a "better" way (also might be easier and apply to future problems) to solve it. You might also want to provide us a little more information on your network situation (OpenLDAP, AD, NIS, simple 2 system sharing, etc).