I was left a little disappointed by my solution for the grass, so I invested some effort into finding a better way to do it.
Not only have I redrawn the texture for the grass to help it suit the style of On Call, but I've also found a far better shader. The new shader still casts shadows, but now has a more consistent, less patchy look.
I'm also currently reviewing the mesh for the grass, as I have concerns about its performance... I will test it on the Vita within the next few days to make sure, but the level is coming along well.