Originally Posted by the_bird
Would the rind of the grapefruit give you the flavor you are looking for? With oranges, there's a lot more flavor in the rind (just the outer, colored layer of the peel) than in the juice; wondering if the same holds true with grapefruit.
Yes it would, all citrus fruits have oil glands in their skin that hold the flavor. As you mentioned though stay away from the white pith.
I also read in Dave Miller's Homebrewing Guide that the pH in wort can be low enough to convert table sugar to invert sugar if added early enough to the boil.