Hi Nathaniel,

I just melt some beeswax in a pan. Put a top bar on a tray to contain any spilled wax. And use a spoon to pour it into the groove. I'm not too careful about it.

After it solidifies, I take a hive tool and scrap any excess wax off the top bar leaving the kerf filled with beeswax that is flush with the top bar surface.

Regards
Dennis