Maybe you could get around the external weight regs by building up a rather robust looking head of fine lead wire then dubbing over it???
Don't know if this meets your regulations out east or not?
Just a thought ?
Even if you could wrap some wine bottle sheet lead around the head of the fly like a slip on collar then finish over it with some materials, maybe double the lead sheeting if more weight is needed to reach the desired effect??
Tight Lines and Screaming Reels!!!