Take out a floppy drive and use the 3.5" bay to mount the hard drive, or take out the CD drive and use 5.25" to 3.5" converter brackets to mount the hard drive there.
IIRC, GVP released a HD mounting plate for the G-Force cards, in order to create the same effect as how the drive is mounted on A2091 controller, however nowadays these are kind of hard to find.
