So, what I would do, print it on our Agfa, use white ink and set it to a variable pixel mask. Then the top would be opaque, but the bottom would fade out to clear - the white would only print behind the pixels, and as the color thins out, so would the white. I know Stacy is grateful that I have explained this, since she does not have this kind of printer or capability - but I would think Signs 365 could do this... not sure, as we don't order from them.
OH wait, that won't work because of the white lettering. and the white rims Burton pointed out - so Nevermind.
The white would have to be set up in the artwork as a spot color - duplicating the gradient. I wonder how that would work - now I have to try it to see if it's even possible.