I've rehabilitated a few "pinky"s...one side note, is just like a mother licks newborn pups and or mama a kitten , to stimulate urination and defication (pee and poo)...squirels also do this. When it starts peeing and poo'ing on its own, you will see the wet spot and the poo , and no you no longer have to do this.
The way you can "replicate" mom, is get a tissue, or washcloth, get it wet with WARM water and rub "gently" across the paticulars. You also want to hold something underneath it or around it...as you WILL get peed on if you do not, (or poo'd).
Its been a while since I've had my pinkys (both of which grew fur, ate regular food (loved dog kibble) and reached the age to BITE, very hard, and thus were ready to go)
They can be really really friendly...and sweet, but if you have no plans to make him a "permanant" part of your family or a yard squirel...please only handle him to feed, facilitate potty...and thats it. Because they do become "attacthed" to you if you handle them too much.
I found it helped to have a MOIST towel over the device in which you house them in.
Good luck. They are so much work in the begining...but it makes your heart smile when you let them go in thier natural habitat and they run up a tree without so much of a blink back at you.