I modified the two regular blur shaders to take a floating point value(.1, .2, .3, etc...) for the blur intensity. Default is 1. Anything higher than that start to look pixelated, so 2 is the highest I'd go.
Modified Blur Shaders (Edit by Ashley: please rename these files before copying them in to your Construct folder - don't overwrite the originals - to avoid compatibility problems)
The blur mask shaders already support intensity. The intensity is based off the lightness of the sprite. A completely white sprite is the highest blur intensity, gray in the middle, and black is no blur at all.