1) Filtering fields - You're right, there is no way currently to limit the fields being returned by the service on an operation by operation basis. You can, however, limit the fields by adjusting their visibility in the source map document (.mxd or .msd). The service will honour your settings and will not return invisible fields. Keep in mind, this will affect other operations too, such as Query, Find, etc
Another option is for you to manually filter the fields in your application.
2) Renaming fields - You can specify user-friendly aliases for the fields in the source map document. The service will then return these aliases instead of the actual field names.
The other option is that you manually substitute field names with user-friendly names in your application.