Why do you feel that you need more than three shot? If you can't do it with three, two more are not going to help you much. The Ranger autos were made to hold only three shells. If you ever hunt ducks or doves (or any migratory game birds) then by law your gun must not be capable of firing any more than three shots.
If you don't want to spend (much) money on it you can buy a dowel that's BARELY smaller than the id of the mag tube and pound it through with a mallet. I did that to a mag tube before and it worked great. You don't need a long one that's the size of the tube...maybe two inches. Then use a smaller dowel (not to much smaller...1/8-1/4" difference) otherwise if you run a full length one through the tube it will get stuck.