No conversions required, if you’re willing to have two Beeminder goals, one for pomodoros and one for minutes. Set an IFTTT recipe to add 25 to the ‘minutes’ goal whenever there’s a datapoint in the ‘pomodoros’ goal.
Obviously that doesn’t work if it’s possible to add more than one pomodoro per day, and probably does Inappropriate Things™ after a pomodoro derailment. (So don’t do that.)
But you can use our IFTTT PROD macro to do this, adding PROD[25,{{DatapointValue}}] to the minutes goal.