Scale particles along shared (non-local) axis?

[mitchfx]

I'm looking for a way to scale particles in non-uniform amount along specific axis based on the TyFlow parent system or another helper's axis, NOT the local axis of each particle.  In other words, imagine a volume of particles born then assigned random rotation...then scaling them all in a common X axis to stretch them out along the same vector.

[tyFlow]

There's no built-in way to do that, but you could do it with a script operator. If I remember the math correctly, you'll want to multiply the particle TM on the left hand side of the stretch TM (or vice versa if I got it backwards). Then assign the resulting TM back to the particles.