Don't even need an addon. Slap this into a macro.
Code:
/run DoTradeSkill(GetTradeSkillSelectionIndex())
/use 0 1
/run ReplaceEnchant()
Then put the item you want to enchant in the 1st slot of the backpack, open your enchanting window and select the enchant you want to do by highlighting its row, and then press the macro - no dialog box accepts required. Just be very careful, because if you press the button with bad timing and the first line fails (i.e. trying to enchant throws an error - moving, already casting, etc.) the second line will equip the item, and you might end up putting a low level enchant on your good gear.