In practice yes, but its not the perfect way. (The x<0 can only be set up under model inputs and affects expo and stuff, so you can have expo under throttle and linear under braking, but there is no slow up setting there.)where it wont impact the reverse to neutral
So I can only think of a momentary button that switches from normal throttle channel to slow up throttle channel when pressed. (Just hold it pressed when you need it) In my use case, I prefer to switch from "launch control" to normal throttle quickly anyways.
Here is how one can setup this "compromise":
Press MDL go to the mixes page - long press and edit the throttle channel - set your slow up - set the momentary butten you want by pressing it.(arrow down and S for slow can be seen)
To have normal throttle while the button is not pressed: long press and copy the channel - remove the slow up - set the momentary button to its opposite setting (arrow up for not being pressed down)