Run yourself from an alternate account or have a friend run you (you will need to make it worth their time as being ran by a high level makes the new personal loot system even worse and typically take longer to get a desired item). I'm not entirely sure but it seems to be that they must be on your realm / connected realm(s) as that's a normal requisite for normal enchanting to work.
I will explain it from the PoV of doing it yourself via double WoWs running:
Once the item drops on your 60, trade it to your high level character that has Incendiary ammo in their bag. Get a new trade window open between your twink and high level toon. From your high level, place the gun in & out of the trade window (I'm told this removes any need of the "are you sure you want to trade this item" button in the transaction). With the gun back in your bag, start applying the ammo attachment & put it back in the trade window ASAP. Swap to your twink ASAP and click Trade. Swap back to your high level toon and click Trade towards the very end of the ammo application, like literally 95% or so (no, not 85%, not 90%, like the VERY end). Shoulder & Leg kits are a 5second cast, so there's ample time. I assume the scope is the same. There are 3 potential outcomes: you time it wrong and apply the enchant without trading, and it is now bound to your high level, you time it wrong and it simply doesn't apply (and can just be retired), or you time it right and your twink receives it with the enchant.
I'm not sure why this subject is so cloak-and-dagger, I'm not the only person who knows how to do it but nobody is willing to explain EVER. Same way you can put nice shoulder inscriptions (or even a ZG enchant if lucky enough) on dropped shoulders, strong leg kits on dropped legs, and even engi tinkers on dropped belts. You can apply belt buckles as well but the socket isn't functionable below 70 as far as I've seen.
I'd recommend SS'ing this explanation because it may be removed on terms of exploitation or salty twinks wanting to keep this secret in their dying game lol. Some of the names in the "users who have read this thread" section know how to do this and totally left you hanging.