You can try over powder wads but I would not bother. More likely to hurt accuracy than help. Need shallow grooves too. Over .010" deep is a waste of time. I would prefer 10-12 grooves and very narrow lands for this work.
People in the past, like Samuel Baker, learned the hard way that conicals REDUCE effectiveness of most MLs. He did not think that conicals were suitable for dangerous game.

Baker's writing in the "Field" magazine MArch 23rd, 1861 is quoted in "The Sporting Rifle and its Projectiles" by Forsythe.
" I strongly vote against conical balls for dangerous game; they make too neat a wound, and are very apt to glance on striking bone."
He then details having a 4 ounce conical mould made for his 21 pound rifle that normally used a 3 ounce belted ball and 12 drams of powder. A rifle he said "...never failed to floor a charging elephant"... "...instead of rendering it more invincible, it entirely destroyed its efficacy, and brought me to such scrapes that I at length gave up the conical ball as useless."
Shoot well hardened round balls w-w or heat treated w-w, this is why you need very narrow lands. You don't need or want a conical with a rifle of this ball weight.

Also see Greener's "Gunnery in 1858" pg 404 (again from Forsythe). He details the conical's "problems" as well. This time in relation to people shooting seals.

Dan