Flat sewing/weaving of a leather scabbard?

One of my friend wants me to do a complete scabbard for its larp sword. I have done one for myself before with a flat sewing (picture attached) and it was very tedious to do but it was a small scabbard.

I don't see how that's possible to do that with a complete scabbard as I won't be able to put my hand inside the scabbard.

Is there tricks for that? Maybe with weaving instead? Most scabbard I see are sewed on the side which he doesn't want.