What you are trying to do is very possible. I dont do mine this way though because I tend to have higher latency and sometimes the game isn't quite ready for me to be able to send the key and it 'misses' my lava burst etc even with generous values. Because of the /click fallthrough behaviour this would catch issues like this and cast it next anyway.

I might look into this further now though if the reports that click is screwed is true.