Create rows in alternate tables

I've looked everywhere I could think, but can't find an answer to this

I'm writing a Rails application that uses an arbitrary number of
groups of 4 tables, each group belonging to a user. Now, I want to
insert new rows into the user's own tables, rather than a single
global table. Thus I cannot just use the set_table_name method to set
a table name, since it would affect all inserts from all users, and I
want it just from the current user, generated at session time.

Is there a way to do this with Rails? I can only find information on
querying alternate tables, not inserting into them.