The soundfont has to be loaded into memory on your sound card, and AFAIK, the only cards that support this are old AWE cards and the SoundBlaster Live!/Audigy series.
You may have have "Soundfont MIDI (Creative AWE32/AWE64)" as a choice in FF7Config but it won't work properly unless you have a sound card that supports it.
If you don't have a sound card that supports it then I don't think there's a way for you to use the soundfont.