I pushed a refactoring in 4b9f18c53139a2dfe616850146d95f49c343c7bf which should make it easy and painless for you. Here is a complete usage example. 

~~~~python
global !p
from vimsnippets import complete
endglobal

snippet test
$1`!p snip.rv = complete(t[1], ["apple", "ananas", "banana"])`
endsnippet
~~~~

I am fine with submitting as is though too and improve later. Let me know what you want to do.