cast only on cooldown?

Warlock Archive Patch 8.0+
1

I would like to do something like this…

#showtooltip Immolate
/cast Dark Soul: Instability
/cast Immolate

but in WoW it will just stop

even /castsequence Dark Soul: instability won;t work

I am looking to cast Dark Soul only on cooldown and then cast Immolate the rest of the time

any help is appreciated

Thanks

MJ

2

assuming you are using gse

ive put mine in the Premacro box with an innerloop limit of 2
just using:
/cast [nochanneling] Dark Soul: Instability

and it works like a charm