Control Spine Direction - Birth / Target Bind Order?

[mitchfx]

I'm working on a setup based on Nickolay Shchetinkin's great electrical arcing example he shared on the fb group a little while back.  What I'm still trying to figure out is how to get my particle binds to always be in Birth-to-Target order so the splines go one direction.  Right now it's random, with about half of them going each way.  In the Max scene I've attached I want the taper to always start at the Birth particle (yellow sprite display) and end at the Target particle (blue sprites).  Thanks in advance for any help on how to achieve this.