True, voting for an alternative candidate will take a percentage of the votes away from Clinton or Trump, and having them win by a lower percentage would be a satisfying way to sock it to the system and send a message. (Although, knowing the media, if the stats started to look bad they would probably start reporting Clinton and Trump vote percentages only as percentages of the Clinton+Trump votes, rather than as percentages of all votes...)
But wouldn't it be wonderful if one of them "wins" the job by receiving support from only a small fraction of eligible voters? I think having a President elected by only 15-17% of eligible voters would send a pretty good message.