I take my garters for a walk now and then too!! I let them climb around in the little mimosa tree in my yard -- it's small enough that I can fish them out of even the top branches.
I don't think it stresses them out at all, in fact, they seem to love it. Much more space to climb than in their tank.
Congrats on the new addition. I know absolutely nothing about ball pythons, but from what I've read, they aren't very active, and you may not get the 'hanging out' experience you were hoping for, but hey, it's worth a try!
And you're little jungle girls are extremely cute!
