So far there have been some intersting responses, I look forward to a great discussion!
Against 1.e4 e6 2.Nf3 c5!? I am not unhappy because I either play the Open Sicilian or sidelines like 3.b3 or 3.c3.
After 1.e4 e6 2.Nf3 d5 3.e5 c5 4.b4 cb4: then 5.a3! seems the only playable move as Bosch shows in his article about the Wing Gambit.
5. ... d4!? is indeed quite a tough nut to crack (in terms of playing for a win). I think that black is already better after 6.ab4:?!, so I would head for 6.Bb2 Nc6.
I would not call it a forced draw, if white doesn't want to take any risks and is satisfied with a draw, he may play 7.Bb5 Bd7
8.Qe2 which looks good but with accurate play black can draw. So if white wants to fight for an advantage, he should either try 8.0-0 ba3: 9.Ba3:!?, which results in an unclear position, but I don't believe that much in the white position.
From my point of view a better try would be 7.Bd3 when white doesn't immediately try to win back the pawn and instead focuses on quick development, which should give sufficent compensation (I liked the white position in Gajewski-Szromba,2001).
Concerning Inn2's suggestion, I'm not 100% sure what you mean but I think my guess might be right.
After 1.e4 e6 2.Nf3 d5 3.e5 c5 4.b4 cb4: 5.a3 Nc6 6.ab4: Bb4: 7.c3 Be7 8.d4 f6!? (Last time at the bookstall I spotted "Play the French 3" and was quite curious what Watson advocated against the Wing Gambit
) 9.Bd3 fe5:
10.de5:! (it is important not to trade pieces because this makes development harder for black, who has less space and not so many good squares for his pieces) Qc7.
Now Watson only gives the weak 11.0-0? Ne5: 12.Ne5: Qe5: 13.Re1 Qc7 14.Bb5+ Kf7 -/+ when white lacks sufficent compensation for 2 pawns (Hamed-Garma, Novi Sad Ol 1990).
So white should either play 11.Qe2 Bd7 12.0-0 (12.Na3? Nd4!!) with very good compensation, it's not easy for black to finish his development or 11.Bf4!?.
It is very interesting how Salmensuu plays this type of position (though he only encountered 10. ... Nh6), he has 3,5/4 with white.
And with the "legions of French players" you're also right, guess how many times I had that in online blitz?
And finally I come to losetowin's suggestion.
4. ... b6 is a sensible idea, black accepts a slightly worse position, but at least he won't come under heavy attack very soon. Perhaps from a practical point of view this is most sensible, as the occuring positions might be to the taste of most French players.
But I wouldn't be unhappy either after 5.c3! Qd7 (5. ... Ba6?? blacks main idea doesn't work immediatly 6.Ba6: Na6: 7.Qa4+) 6.a3 Ba6 7.Ba6: Na6: 8.d4 += when white can claim a slight edge.
Hope this wasn't too long!