It’s not really possible right now, as there’s no channel subscriptions endpoint in Helix yet. With a bit of luck it’ll have some of this sort of functionality as the old v5 subscriptions endpoint was very lacking in several areas.
For channels that log subs themselves it should be trivial to calculate the number of gifted subs by each user just by aggregating the logs. Those who don’t track that sort of data themselves though are out of luck. You could collect the data going forwards but you’d be missing out on historical data so numbers wouldn’t be very accurate if you’ve had a lot of sub gifts prior to that.