I have not seen the movie, but when I was dabbling in special effects and theater make up, there were sideburns and other facial hair you could buy then trim and use spirit gum to apply. The hair is on a mesh like backing, so you can easily trim it. It is real hair, so it can be dyed but also comes in about 5 different colors to help match to your own hair. The set runs about $16.00 I think. Spirit gum and remover runs less then $7.00 for both bottles normally. There are a few online stores that carry these items also.
If you are stuck with Halloween stores because you have no theater stores or can't order online, you can also use crepe hair, but it is a royal pain even if you have worked with it before because it is artificial, comes braided so you have to iron it flat and looks best as very short hair or stubble, but hard to apply well because it is used with spirit gum also.
Other then that, you can make sideburn pieces out of panty hose and natural hair, but I don't suggest it because it takes a very long time. This technique is not used anymore because of the other pieces that are commercially made and at low cost.