Material based on distance to particles

Can anyone suggest a way to create a falloff material based on surface 
distance to particles?
I'm after the effect you get from the falloff map using the distance 
blend->object mode, but rather than being based on the distance to one object
I 
want to base the falloff distance on all particles in a system (or at least, 
objects I can hang off all particles). I've attached an image showing what I 
mean. The particles would be spawning at different times and the falloff 
radius would be per particle and animated based on the life of the particle, 
it's basically a creeping effect.
I suspect it's a scripting job, but my skills there are quite limited, and as 
usual it's a ridiculously tight deadline ;) Any suggestions for 
alternative methods for achieving the same result would be gratefully
appreciated.
Thanks!

you could try to use this scripted controller, which controls an object by 
particle position

http://www.monkeylab.com.au/rd/Overview2.html

And then use a script controller for the mateial's color, and make the color 
dependent on the difference between the particle object's position, and the 
colored object's position