Also, if it is thick enough, fill it and use Saran Wrap over it. Another more complicated way is to make a trough of sorts with a movable "card" that is 45d off of the vertical. Then you pour enough to cover about the bottom half, the fold that card up to vertical. That should help push it into to knot. Then clamp.
Does it have to be epoxy? Do they want to hide the know or accent it without it failing later?
If they want it filled and smoothed, I would use timbermate or something more "solid" to fill.
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