You don't need a script extender if you do it with different objects. You may need a script extender if you do it the way the OP described (a single .NIF file with all the different weapon models added to it and shown/hid at will) - not even sure if that's possible at all even with a script extender. Making it placeable is much more difficult, of course - I'm not sure why you'd want to do that anyways, since the thing would be the size of a medium-sized room.
You don't need it. I have a wall gun rack in one of my FO3 mods. I did this for my modded guns.
This is what you do:
Make an activator out of a wall (or some flat surface, I used woodwallchunck01).
Whatever weapons you want displayed on the wall, open them up in nifSkope and remove the collision mesh and save them as weapwhateverStatic. That will make them static and you can place them anywhere you want and they won't move. Make sure you remove the clips, looks better.
In the GECK, use static guns to create activators, and position them any way you want them on your wall (activator). Make sure to give each a reference, as you are going to need that in your script to "mount/unmount" the gun on/off the wall. Also, make sure to select "initially disabled" so they won't show right away.
Now for the scripts.
Each gun gets a script.
The wall gets a script.
The wall script looks like this:
scn MyGunRackScriptBegin OnActivateIf player.GetItemCount AA12shotgun == 1 player.removeitem AA12shotgun 1 AA12ACTREF.enableEndifIf player.GetItemCount My44Magnum == 1 player.removeitem My44Magnum 1 My44MagnumREF.enableEndifIf player.GetItemCount UrbanSpecOpsSniper == 1 player.removeitem UrbanSpecOpsSniper 1 UrbanSniperRifleREF.enableEndifIf player.GetItemCount MyAssaultRifle == 1 player.removeitem MyAssaultRifle 1 G3AssaultACTREF.enableEndifEnd
One of the gun scripts looks like this:
scn UrbanSniperRifleACTScriptBegin OnActivateUrbanSniperRifleREF.disableplayer.additem UrbanSpecOpsSniper 1player.equipitem UrbanSpecOpsSniperEnd
What happens?
When you click on the wall and you have the gun on you, the gun is unequipped, and the static reference (mounted gun) is enabled.
When you click on the static/activator gun, the static reference is disabled and you are equipped your gun.