The best option I can see in this is to buy yourself an eShop redeemable card.
Go to your friends, ask him to play a bit on the Switch, but instead enter the eShop, redeem the card and download Snake Pass with the card's points.
I am not sure how pricy Snake pass is, but I assume maybe a 10$ card might do it since it's an indie game.
And you might have some spare points in the account as well.
Sadly, that's the only option I see if you really want to force that game as a gift, because Nintendo currently has no gift system in the eShop.
It's one of the things that just baffled me about the current eShop system.