Some players love getting Volt Speed buffed; others beg him to stop. Being able to backflip out of it is an imperfect fix imo, because the duration on it is so low that the Volt will have to constantly recast it. Having to backflip every 20 seconds can feel intrusive. (He shares this problem with Limbo, and his version is even more restrictive.)
My solution: When you tap Volt's Speed, it still casts without an animation as it currently does, but it only affects him. When you hold it, it casts with a one (or maybe two?)-handed animation and affects the squad as it currently does. Maybe he exaggeratedly points forward like 'Chaaarge!'
This way, if a Volt player is using Speed for themselves, it will be as seamless as it ever was -- but if they want to buff the group, they have to commit to an animation. (Otherwise players would just invert his tap/hold settings and continue tap-casting the group-buff as usual.)