Hmmm, I don't know about the hairline. It might turn out looking tacky but hair grows back. You could give it a go.
As for sideburns, I've heard someone trying rogaine and being successful but it seems like a really risky thing to do around that specific area. I wouldn't do it. But sideburns can be faked, sort of, if you let your hair grow down a little and square it off. I wouldn't expect you'd be able to do something like mutton chops, but you'd be able to extend it a little.