Kitchen Island Hood Install Help

Hey all,
I'm trying to figure out how to install my kitchen island range hood.  I have the orginal fan still in the ceiling and the motor to the new fan is built in.  I figured I could just mount it to the ceiling and use the existing hole for duct along with the wiring that is already there.  My question is how would I mount the unit to the ceiling without the extra support?  I'm trying not to cut anymore holes in my roof.  Any suggestions would be grateful.  Or if anyone know an installer in the San Mateo area.
Thanks