This should do the trick:
Database::instance()->query(NULL, 'raw query here');
Kohana's ORM does not have the capability to create tables for you. You can define the columns manually, but if I recall correctly not with enough information necessary to recreate the table.
I've seen two ORM's made for Kohana that could create tables. They were Sprig and Jelly if I remember correctly, I don't think they are maintained anymore though.