Help with a Casiotone MT-140

So I found this thing in my in-laws basement and lo and behold it has some killer tones (ok, like 3 or 4) - anyway, does anyone know a simple way to mod it so I can control the tremolo? There's a great chorus sound but it's got it's own tremolo and I'd love to be able to speed it up or slow it down. Just thought I'd throw it out there