You can do this by having someone lay down next to a car/ledge or have someone stand under a roof with you above them, but the ladders work the best.

Use a class with Claymores and OMA.

Have a friend (or enemy) climb halfway up a ladder. Stand above them so that when you drop a Claymore, it lands on them.
This will cause the Claymore to launch somewhere else; it may go 2 feet or it may launch over a nearby building.

Just keep OMAing into the same class and dropping Claymores.

Remember that you can only have 2 at once, the oldest ones will explode as you place new ones.

With practice, you can anticipate where the Claymore will go.