In the rental property I have I have our carpet cleaning company stretch carpet if the unit calls for it. If you have a carpet cleaning company ask them if they do it. It will probably be the only time you need to stretch it before you someday replace it. Not all carpet needs to be stretched, and definitely not on a regular basis, so I wouldn't bother investing in a knee kicker for this one project, but if you have one or can borrow one you won't hurt anything by giving it a shot.