Hmmm... Lay on Hands used offensively is very, very similar to range: touch spells.
How about this:
It seems to me you might be able to use Lay on Hands and "hold the charge," delivering it the next round with an unarmed strike and then do unarmed strike damage, Lay on Hands damage AND Smite damage.
It's a very minor stretch of the rules to do this, and it is balanced by the required use of two actions in two rounds to accomplish it.
It's not really technically legal, though, I think, and certainly is not as good as allowing Smite to combine with the offensive use of Lay on Hands.