This is a really simple modification!
Step 1
Find:
player:AddCleanup( "props", newent )
At or near line 121.
Add after that line:
gamemode.Call( "PlayerSpawnedProp", player, ent:GetModel(), newent )
Step 2
Find:
if ( !self:GetSWEP():CheckLimit( "props" ) ) then break end
At or near line 68.
Add after that line:
if ( !gamemode.Call( "PlayerSpawnProp", player, ent:GetModel() ) ) then break end
You're done! Told you it was easy!