I've played several FFA games with players that are far better than me.
The strategy I used was simple. Sit around, don't be annoying and wait for your chance. Now if everyone would be doing that, you'd have a problem, but I like the idea very much. However, if you're doing battle in FFA games and suddenly (when the second to last player dies), your final opponent appears to have 20 GCs or a lot of soul rippers, then you haven't really been paying attention. If you're fighting against your best rival, then he won't be your best rival at some point any. That's the moment you're going to have to be careful for because changing targets before that is too early, but after that may be too late.
I've got an example here, but it's from the ancient pre-FAF period, so if you want to watch the replay, you'll have to do that with the old FA client (Rock and me are with FAF currently but I have no idea whether the other two are still around). Additionally, several critical mistakes were made (The UEF player not building T3 PD to completely annihilate me being one of them) but I think this game is still very enjoyable.
http://dl.dropbox.com/u/80253546/FFA%20HH%20Rock%20Sifnoc%20Plasma_Wolf.SCFAReplayNote: the file is 2.5 MB (the fafreplay sizes are much better), which is why I couldn't upload it here as an attachment (2 MB limit).
On the other hand, I must say that there's a big chance sludge won't be fun playing as FFA because it's so small. If you're playing an 1v1v1 on a larger map, the best player might be able to withstand the two lesser ones. On sludge, he just doesn't have the time.