Client-Only Database Field in a Database from a Publication

We have a table of items, where you could select each item and then perform bulk operations on it.

Would it be possible to do the selection of the data with some client-only database magic? e.g. a database field that could be set in minimongo and also queried but will not be present on the server?
If this would be possible, we could do a lot more in this way, saving a lot of ReactiveVars and ReactiveDicts as well as combine a lot of code in just using Database Queries.

E.g. the data looks like:

user: {
  "name": "John Doe",
  "email": "",
  "stuff": "stuff",

where the client is not allowed to update the fields (e.g. all updates are denied), but there is however a database field selected that is not part of the schema (or the schema tells, it is client only) and will not be mirrored to the server but will be available for queries on the client.