I have about 25 ficus of varying species & I only acclimate the best bonsai trees. The rest I move directly into full sun, where the leaves burn & drop. They are quickly replaced by new leaves that appear, already acclimated to the additional light. It doesn't seem to bother them much, but my trees are usually growing with good vitality after a winter under good light & in good humidity.

There's no sense in trying to minimize damage now, except for the fact that it's too cold at night for your plant to be outdoors - prolly during the day soon too (cooler conditions predicted in the Midwest). If it was warmer, I'd tell you to leave it outdoors in full sun, but you should bring it in anytime temps will drop below about 55*.

Your plant is likely very weak now - probably at its lowest energy level of the growth cycle, even before the loss of foliage - and in danger of attack by insects or other pathogens. It could also die if it doesn't have enough energy to push a new flush of foliage, but since you mentioned that there are still viable leaves, it will prolly be ok. It's very important however, to make sure that nothing happens to the new flush of growth. It's almost a sure bet that the tree will not have energy to produce a second refoliation.

Al