My idea was for a dagger with a hollow handle, you unscrew the pommel and it has 2 clips that hold a small vial of poison. You then screw the pommel back in and it clicks, when you are ready to use the poison you give it one more twist and a needle inside of it punctures the vial and lets poison run through to the blade and out small holes thus poisoning the blade. This could be used with any kind of poison and could even lead to bolts that do the same with small poison vials inside bolts, or even swords. Could be partial crafted by a weaponsmith and then modded by a tinkerer. Just an idea I have had for a while
Heitak