Read about Charlemagnes Paladins. The were far from the "idealized" version in D&D.
Anyways, I don't expect their code to make them do stupid things or to cost others their lives. So as long as the player can show that as their motivation to play loose with their code, I let it fly.
I also allow Paladins to use poisons, as long as it only disables, and those affected are taken prisoner, not killed.
If such prisoners are later executed through "due process", everything is fine.
Paladins have no problmes withothers using poisons in similiar fashion either. So, as an example, the thief in the party can use poisons that disable, and make themselves more useful in the combat as a result. As long as those poisoned are then taken prisoner and dealt with in the proper manner (Due process, whatever that may be in the campaign) the Paladin won't care. Not enough to cause party conflict, anyways.
Plus Paladins should offer surrender, take prisoners, and encourage conversion or change of loyalty to the "proper" cause, etc... whenever possible.
Heck, I even have a handful of "converted" orcs and other goblinoids in my campaign, as a result fo this. They often get training in a "class" of some type and then serve the Paladin, at least for a while. Partly due to the Paladins kindness, etc... and partly because the goblinoids quickly realize that they can only be a part of civilized society (easily, anyways) while close to or directly in service to the Paladin who converted them.
There is even a converted Frost Giant in my camapign, who rode a Mammoth (fans of "Against the Giants" probably know who I am talking about). He died in service to the Ranger. He was then reincarnated by the Rangers Druid friend, into a pixie.
Yeah, I have a lot of fun with this kind of stuff.