Sveta, I think you're overcomplicating. Why is any second blast needed? KB itself defines a movement rate. KB has a damage factor...1d6 normal for every 1" of KB. Or, if you prefer, call the inches of KB a velocity, and the sucker hit by the blast is doing a Move Through with velocity == KB, while using 0 STR, on the secondary target. No additional energy from the attacker is involved, so why is there a second Blast?
massey: the conditions on the secondary attack are very complex, and there's no fixed damage per se.
This is really a skill-based power stunt. So I'm thinking...yeah, ok, a CSL has to be used. It's not bouncing the power per se but it's similar enough, so in order to have a chance to hit the *second* target, treat that attack like the bounce. THEN, it needs a skill roll to aim. Anything representing that kind of sense of direction (and absolute direction sense might help). The roll has a range mod based on the entire distance...you to target A, then target A to target B. Last, perhaps an ad hoc -1 or -2 penalty on the roll because target A is hardly a precision missile weapon.
THEN...if target A's body hits target B, the damage is as if A did a Move Through on B, as noted above. With full effects on both A and B...which probably means nothing serious, since A's velocity-based damage is not going to be high. Realistically, the hope wouldn't be to do a lot more damage...just to knock B down too.