Dreev is going to post the usual link to Fake Data is the Devil. He might consider even bringing up the idea that one could change the trigger and game the system an ‘info hazard’ (As in, the average Beeminder user is never going to think of anything like that by themselves.)
In my opinion, hardening goals is good, and we should be able to rely on technology instead of will power (otherwise, what’s the point). I think you are on the right track with making access to IFTTT harder.
One approach could be to purposefully lock yourself out of the IFTTT account (and related e-mail addresses so that you cannot reset the password). You could do that by giving the password to a trustworthy person and deleting the password on your side. You would then have to ask them for the password to regain access, or you could use a timelock to manage the lock out by yourself.