You can push boars by walking into them while they stand still, but this is only good for short distances. You can build a pole fence around him and "guide" him back home. Fence a narrow path back with food along the way, but again distance and patience is at play here.
There is a harpoon you can get later, but it does damage and not sure how well it work. Never used it.
I use a mod, Valheim Plus, and an option is to make your tamed pets invulnerable to everything but your meat cleaver. I use that now and when my pigs got out they were very helpful in raids and clearing wandering mobs. Nothing can kill them so they run interference. Very satisfying having a pack of watch pigs take on a skeleton invasion.
You could do something like that and know where ever Boris goes he will be safe.