I've run plenty of Lurker lists that carried no close-combat weapons... They either do their job or pay for their failure, like any good cultist should.
"Unarmed" is just a good part of the game's balance even though I agree a rifle butt makes a convincing club.
But if I went the route you are suggesting, I would be tempted to just count the figure as not being 'unarmed' and give it no CCB or DAM bonus.
However, I would also add a skill to the list, something along the lines of bayonet drill, that would allow a figure with with a 2 handed rifle or similar to fight as if equipped with a spear.
That way a model could start with the skill, or you could earn it along the way, and the value of close-combat weapons isn't discounted too steeply in the early campaign.