QSqlRelationalTableModel - two references to the same table

Hi,

Is it possible to set relations to more than one field in an other table using one foreign key?

Having two tables: x (id, y_id fk y(id), ...), y (id, a, b)
and X class which is a subclass of QSqlRelationalTableModel I do:

setTable("x");
setRelation(fieldIndex("y_id"), QSqlRelation("y", "id", "a"));

Now, if I try:
setRelation(fieldIndex("y_id"), QSqlRelation("y", "id", "b"));
the first relation will be lost... And I need to put both fields - a and b from table y to my view.

Is it possible at all or should I subclass QSqlQueryModel, instead and implement my own setData etc?

Thanks in advance for any help.
Adam