We were discussing this on superuser:
http://superuser.com/questions/424837/setting-environment-variable-for-launchctl/424847

Never heard back on the results of my proposed fix, but I do think it's the right one.

Short version: find the line that says:

my <at> args = ($ENV{TODO_SH}, "command", "add", $add);

and edit it to read:

my <at> args = ($ENV{TODO_FULL_SH}, "command", "add", $add);

FWIW, I wrote the plugin, and I'm running OS X - but I launch it from a cron job, via scripts that make sure my path is set up just as it would be at a normal bash prompt, so I never ran into this problem while testing.

-paul