Converting an AT-4 spent launcher for nerf rockets

A couple of birthdays ago I received a spent AT-4 launcher. I've been toying around with the idea of converting it to shoot nerf rockets or other items for fun. I have made my share of potato guns and such but I've always used flammable materials to fire them. As I understand, these spent tubes are worth quite a bit, so I would rather not do any permanent modifications to it. I was thinking to have some kind of separate pvc setup that I could slide inside the tube and use it that way. I'm not too skilled with pneumatics, so any ideas or help would be awesome.

I'll be working with this over my spring break to see if I can get it ready for the Op Noob. I'm waiting for a reply from the Bad Karma field we will play at to see if they will allow it.

I've got pictures of it somewhere I'll post when I find them.

12g CO2 capsules are amazing. Just need to have some sort of way to puncture the capsule.

i got an old paintball gun that might be able to do that, with just the internal mechanics