Your best IMP play is to cash three rounds of hearts, discarding a club, cross to the ♦ K, leading the jack as West may cover. Assuming no cover, cash the ♦ A and exit a spade. In order for West not have to cede the contract immediately, he must have started with precisely three low diamonds.
If you are that unlucky, West will exit a diamond to East’s queen, and you will have to deal with East’s presumed low club return. Good luck.
Notice that you are far better off adopting this line of play than taking the diamond finesse. If the queen is onside, you make 4♠ whether or not West covers. If the queen is offside, you are far better off playing the ace-king as East may have started with Q–x or Q–x–x–x.
The recommended line of play has a good chance of finding West short in diamonds because East started with a singleton spade and figures to have the diamond length.
Thanks to Ron Popp of Arlington Heights IL for this one.