Last time I did this I used two funnels:
I took a funnel with an attached 2' long flexible plastic tube and shoved the tube into the fill hole, then stuck the funnel end under the battery, but visible from up top. The plastic tube was springy enough to keep it in place.
Then I used another funnel between the battery and the headlight assembly to direct the fluid into the bottom funnel as I poured transmission fluid into it. I had to be careful to not let the bottom funnel get too full as it'd fall from the weight.
