Soo... I've been browsing through the scripts for a few hours now, the only relevant parts I found were a couple of checks in effect_enchantment_h.
If I remove them, I get visual effects on ranged weapons (flaming bow and mage staff... looks dangerous for the user

) and added properties display correctly on the item, but of course nothing special happens when the weapon is actually used.
I only tested this with the flaming weapons buff and a random poison, but I assume nothing at all works ? Is there really no way around this ?