Keeping the protective plastic on the product...

I have a really cheap cell phone & I want to keep the protective plastic on the screen. It’s already coming off. Is there a way to reapply it so that it’ll stay on [at least for a little while longer]? I really don’t want to have to buy one of the real screen protectors & cut it down ‘cause that’s just too much trouble to be bothered with.
Any ideas?