To store the data back to the field in the list, I guess you would have to use workflow, e.g. when the entry is modified, the workflow starts, trim the leading space of the field, and store it back - and perhaps also send an email to suggest the user not to put space when s/he add new names.
Depends on what kind of workflow you use (e.g. the native one which you create with SharePoint Designer, or 3rd party one like ninetx), there could be different ways.
If the workflow allows regEx, or Trim() function, then the solution would be obvious.