its very easy. register clcmd and in function get players weapon (first check if is alive), to get players' weapon you need privatedata offset of active item (i think its 373) and get it
Code:
#define m_pActiveItem 373
new Weapon = get_pdata_cbase(id, m_pActiveItem);
Bam! now u can set weapons rendering using fm_set_rendering or such thing.
[PS: I dont think if this will work lul]
[Cause weapon has not its model and you see players weaponmodel which is players variable and that means you must set rendering on player]