How to solder micro stepper motor pins?
I would probably use a small amount of tacky flux and pre-tin both the wire and the pins. 

If you can secure the motor in a clamp with pins facing horizontally, that would be ideal for me (an average solderer). 

I would feed the wire with my non dominant hand while resting my palm on the bench top and soldering with my dominant hand.

Hope that makes sense. Pre-tinning will make it relatively easy.