yeah, def take the filter out, -I usually just use my teeth....then replace it with a rolled up bit of cardboard (the roach). I wouldn't slit the ciggy open tho... just roll it between your fingers to get the tobacco to fall all out and then put your green in and push it in with a paperclip or something. Take the filter out last tho or all your weed will just fall through when you're packing it!
Hope that helps mate!