Chromakey using the AW-HS50N

First time I have posted to this forum, though I love reading it. I hope this is the right area for my question.

I use the AW-HS50 in a county government environment to record council meetings and I have wrote custom software to generate onscreen graphics such as current agenda topics and lower thirds. My graphics output is the "second monitor" of my computer which is fed to the switcher with a DVI cable. I'm able to overlay that input over my camera inputs using the built in keying capabilities of the switcher. It works fine when i have my graphics slide into the screen or just appear, but when I fade them in I see the green of the background (using green as my key color) as it fading in. I'm assuming that as the image fades in, the green key color changes enough that it is no longer considered the key and is then shown.

Does anyone have any suggestions that may lead me to a working fade solution or is this just not possible with that hardware. I'm quite the amateur here and hope I gave a good description of what is going on.

Cheers and thanks to anyone who actually read all that.
Lucas