Some bookies have odds on them finishing top five, so you could do that. Though I suppose it is possible Brentford put a good run together and finish above them/us so we wouldn't make it and you still wouldn't win your bet, either.
I was looking for odds on us not to finish top five but can't see them anywhere.
Anyway if you want to find top five odds go onto Oddschecker but best wait until the evening kick-off finishes as they usually take outright offers away while matches are in progress.