Well, as it's already built, it's hard to use spoke-prep or locktite in this case, but what you could do, is put the wheel on a truing stand, and take each spoke, and back them out a SMALL BIT, dab a bit of blue locktite on it (i wouldn't use red, as it's too powerful and when you true or re-tension your wheel you might end up snapping a spoke instead of turning it). Once you locktite it, screw it back into the nipple, and re-tension it until it is trued, dished, and in round properly, then move to the next spoke. Take EXTRA caution when you loosen each spoke as to how many turns you make, so you can make sure to keep it in round. I would also suggest doing one spoke, and skipping a few, and going in a pattern as you work your way around the wheel.
It's a lot of careful and time consuming work would go into this, and I would advise taking it to a shop to have it done, if you don't fee comfortable doing it yourself.
Another option would be, to ride the rims un-locktited, and once the rims set in (the spokes stretch and de-tension) take it to your shop to tension up and have them put a drop on em when they true them up.