Map of other types than Strings in Grails

Question

I created simple domain class with map within it.

class Foo {
   Map bar
}

Bar mapping will be created as sth like:

create table foo_bar (bar bigint, bar_idx varchar(255),
   bar_elt varchar(255) not null);

...as stated in http://www.grails.org/GORM+-+Collection+Types:

The static hasMany property defines the type of the elements within the Map. The keys for the map MUST be strings.

Now my question is - is it possible to create map of values other than Strings? I can achieve that using pure Hibernate (element mapping) - any ideas how to port this to Grails?