im pretty sure there is no way you can insert a pause. for its against the rules.. or w/e..
but..
if you dont mind smashing the same button multiple times.. you can maybe do this...

/castsequence reset=15 ,,Tremor Totem,


by doing that.. it will only cast the totem after your 3 time of pressing the button.. so.. if you smash it 5 times.. it will take it about 1 second of so, to cast from the first time you pressed the button.
any way to add a pause into casting by only pressing a button a single time is against the rules and can get you in trouble. im pretty sure..

work with what you got. search the wiki.. i mean.. im new myself and i find everything i need in there...
its all in there.. : )

well, thats what i think at least. I might be wrong. Im a noob, btw. :P