How to keep a rolled cabbage leaf (stalk leaf not the outer leaf) in place?
Correct me if I'm wrong but you want to make a Spring roll but with cabbage leaf instead of rice wrapper? 
If yes then what you want to make is cabbage roll. 
And it's almost impossible to make with raw leaves. They are to bristle and cook too long to let what's inside cook accordingly. As in it will be overcooked before stuffing will be done. Or if you put ready stuffing it will get soggy. 

What you can do is to boil the cabbage whole and peel leaves that are soft and tender. Then you cut the steam to flatten it (so you cut horizontally).
After that it should be enough to roll stuffing in it and seal it. 

Edible "thread" that you could use is leek cut in length and steamed a little bit so it's softer but still springy.