TL;DR
How about providing TABTAB_AUTO_PATH option as an environment variable?
When it's defined, --auto installs/uninstalls its generated content into $TABTAB_AUTO_PATH.
Long Story
I usually use zsh but also use bash in times and manage them under a git repo.
They only contain common settings and I put all the other local system dependent settings into ~/.localrc.
As a result, my .bashrc and .zshrc both have following lines:
if [[ -f "$HOME/.localrc" ]]; then
source "$HOME/.localrc"
fi
(It seems, as a matter of fact, that people who maintain their own dotfiles repos use patterns like this.)
Accordingly, I hope that every time I install some node packages which use tabtab, I want tabtab generated contents to be placed in .localrc.