From The DarkMod Wiki
Preferable both should be in one file, though.
"model" "models/darkmod/weapons/broadhead.lwo" "clipmodel" "models/darkmod/weapons/broadhead_collision.ase"
It is also possible to name another func_static as the clipmodel.
In all cases, however, the usual D3 limits for clipmodels apply, that means the clipmodel must be quite simple.