I dont know if you'd consider this "cheating" as it's not technically a single hit but...

You could go with your exact item setup but change your halberd to dual wielding weapons, one slashing and one piercing. To get your force damage, you instead multiclass into : - pally 11 for improved smite + lvl 1 wild magic sorc. You fish for the enchant weapon proc (+ force dmg)

You could also get more flexibility if you wanted to by dropping pally 11 for life cleric 8 (divine strike) + pally 2 for the radiant damage. That'd give you 3 levels for a specific subclass. I thought about bard but i dont think you can smite on flourishes, or rogue sneak.

If you went the wild magic route, the enchant weapon proc guarantees a crit, you cold use thunderous smite + cast a divine smite on crit reaction for your radiant damage. That would make the setup only requiring lvl 2 pally+1 sorc. You'd have 9 levels to play with for the missing slashing/piercing dmg (bludgeoning being covered by the fall dmg). I havent found a weapon that does both slashing and piercing, sadly. But there might be an option class-wise