Specifically, I'm thinking about the spell Bestow Grace of the Champion, though this is also applicable to spells like Holy Word or Order's Wrath. If I have a LN or CG character, is there any way to make these spells affect them as if they were Lawful Good?
Anybody?
Imbue with aura cast by a character with the alignment you wish your PC to be registered as.
Alternately, look at the use magic device skill. You can emulate another alignment if you so choose. A DM might be persuaded that the emulation is so good that the character actually registers to spells and abilities that have alignment based effects as though the character actually were of that alignment.
Or you could just have them emulate the desired alignment while casting imbue with aura if that doesn't fly and an NPC with the necessary alignment is unavailable or uncooperative.