The symlink approach is not flexible enough for our situation, but we can tell folk to to use the --data-dir argument. 

Thanks for the help.

On Wednesday, October 18, 2017 at 8:52:54 AM UTC-7, John MacFarlane wrote:

$DATADIR appears in the manual just as a placeholder for
whatever your user data directory is (see --data-dir).
The environment variable has no effect.  I've made a tweak
in the manual to make that clearer.

Note that the default user data dir is ~/.pandoc (on *nix),
so if you just symlink that wherever you like, that's the
most convenient solution.