Permission to Use a Function without having OP

I wanted to set up a couple of function for a few of the main character players to use in our event coming up. I thought I could give them access to the individual function commands through LuckPerms, but it's not looking like that is possible. 
Is there another way I could give a player access to a specific command without giving them op perms? 
I would prefer to not use command blocks because I am hoping they could "use the abilities" anywhere on the map.