My stoker, after riding with conventional bullhorn bars for years, including on two cross-country tours, asked if there was a way to get more palm support.
Sure thing!
Solution: A set of used super-light flat bars, Ergon GP5 grips and silicone grips cut to fit the rest of the bars.
I started full width, about 550mm, for a tryout. I could trim and re-try until the width was right.
She loved it instantly and liked the full length, a bit wider than the bullhorns, as well as the very slight rearward sweep.
We can fine-tune it over the next few-100 miles.
(The Deore XT brake lever lets the stoker control the rear V-brake; captain controls the rear disc brake.)