Ha well even if you can't get it all off in 1 stomp, the duration on shockwave is very generous. If you just land your shockwave on the first stomp and they get away before you can cast boulder, you'll be able to stomp again while the swirls are still active most of the time. Again I really don't know how well stun even works in d2r so all of that may not even be worth it.