Actually if you just keep the current battery(which would be much simpler) you can just connect wires to the existing contact points of the button on the laser. You won't be using the button anymore and probably not the case, unless you take the button out and run the wires through where the button used to be. From there use the wires on the two connector points and run them to your bigger switch, button, push thingy, etc and wire it up to connect when you hit it. Just make sure the previous points don't connect.
I'm not expert but I think that's workable.