When it comes to the Pathfinder Fiendish Heritage and Tieflings, there is an almost universal house rule. Most GMs simply ignore Fiendish Heritage and allow you to select variant Tieflings without need for the feat, like the Pathfinder rules allow for an Aasimar. If for some reason your GM is unusual and requires the Fiendish Heritage feat, then disregard the Tiefling and convert your build to Aasimar, which has similar abilities and stat bonuses. For instance, this Free Paladin Tiefling Build can be easily converted to a Paladin Aasimar.
I guess, should Paizo ever come out with a feat that Aasimars are required to have before selecting variant race heritages, then this universal house rule will go away. Until then, I and many others say, disregard the Fiendish Heritage feat tax.