if you cant get out of your strumming pattern by yourself youll have to either practice the strumming techniques available on this site or practice other peoples songs.
i too only strum a few patterns but i only use the strumming for the rythmn of the song and to get the melody. most of the time i record the strumming on one track then vocals on the next track then turn down the strumming track and then start from scratch with just vocals and melody.
listen to your recorded vocals with your guitar in hand and see what else you can add to the song.
if you just play accoustic i suggest you just learn more patterns cause youll either have to have an awesome rhythmn or melody to get away with one dimensional play
just my opinion though.