Personally, I think you've got it. I wouldn't want a cold dead wedding by the organization book and some Watchtowers written in the 1980's.
I believe with the fait accompli method that only questions can be asked and you can just give simple "none of your business" answers.
Just make sure you have credible evidence to indicate that it was not because of premarital relations or that she is currently pregnant, (unless you are Joseph fathering the Messiah) which means you have to come up with a plan.
Questions will be asked of you even if you have it at the Kingdom Hall, even the day of the ceremony the speaker can ask you if you have "done the nasty" and good lord don't touch her breast.;)
Personally, I kinda like the edginess of running off and eloping. You know witnesses, they will talk no matter what until something else is news worthy.
Basically, you can say, "we didn't want the emotional pressure, the expense, and so forth, so that we could concentrate on spiritual goals, "we are trying to keep our life simple so we can pioneer together", (I've learned what the real meaning of the term, "Pioneering together" means)
You might add that local weddings have become competitive to out do the other and you didn't want to further the competitive spirit in the congregation.
In ancient times a man would just walk through the streets with his wife without a ceremony, everyone would know they were now married.
Make sure your paperwork is together to make it legal. IF, thats what you want to do. Also, There is nothing wrong with having a private ceremony having a person, not necessarily an elder, give your formalities, and inviting only your family.
If you are not currently the object of some "investigation" by the elders for suspicious behavior you will be all right.
Personally, I would give you a greater wedding present if I didn't have to go. I never liked the weddings. They have banished the liquor, dancing, and music at the reception; and drinking with a suit on in your car like you are a teenager is a drag.