A full or half-twist throttle will not work at all with bull horn handlebars. Here's a picture of them set up in a couple of different ways. the one on the right is the way I've done a set but it was quite a long time ago. As you can see you can forget about fitting a grip throttle over one end or the other, and even if you could... how would you actually twist/use it?
Look for something called a "handlebar bob". It is used with road bike drop bars (i.e. :"ram horn handlebars") so you can put a standard thumb throttle on the bars and actuate it with your thumb while holding the handlebars normally (i.e. in the drops or even on the brake hoods).
While you are cobbling together your solution, look for a 'left handed throttle' which is a throttle that has a sort of sideways pull, rather than one that follows the circumference of the bars.
Between the use of one or both of those tools, you'll likely come up with a solution that works for you.
By and large, its not correct to say full or half-twist throttles are in any way the preference of ebike riders. What they are is the default choice for riders who started out riding motorcycles. Its what they are used to so its what they tell people they like. On an ebike they are arguably a safety hazard, as a live ebike has no idling motor so you can't tell if its on. So if you grab the bars suddenly and reflexively (lets say you are standing next to the bike and it starts falling over), your grab can activate the throttle on a live bike, which will take off. If you don't let go your arm is like a tether and the bike shoots up, thanks to your arm, and the momentum carries it up over your head. Gravity brings it down again but not gently.