Werebat
Explorer
One thing I would say is make them see their Intelligence in a different light when it comes to roleplaying and decision making. Have their Intelligence Score relate to the character's IQ. Now that they know this, they have to act out what they think somebody with that IQ would be like.
Yeah, I... The thing is, if you can rely on your players to be constantly "on their honor", even when it is detrimental to their characters, this would probably work out OK. If not... then the DM is going to be engaged in a constant war against the players' shenanigans as they proceed to play their Int 8 characters as though they were in the 12-14 range (or wherever the players themselves are). Until it is to their advantage to act dumb.
In reality, I'd guess that SOME players could be trusted to actually RP low Int characters, even to their own detriment -- but by and large these are also the sort of players would would not be likely to dumpstat intelligence in the first place, unless they really wanted to RP a low-Int character.
If you have a table of five players, and four of them make Int 8 characters (the fifth is playing a wizard), it's a fair bet that not all of them did so because they really wanted to RP high functioning borderline mental deficient characters.