If you have another ability that has a 15 second recast/reuse timer, you could castsequence that with Thrash.

Skull Bash has a 15 second cooldown.
Assuming you don't mind Skull Bash as a regularly used ability in your rotation, you could use that.
You might prefer to save it, as it is an interrupt.

#show Thrash
/castsequence reset=combat Thrash, Skull Bash

If you go this route, probably combine it with a priority sequence.
Where you mash several abilities all at once, several clicks a second.
With the theory that if one thing is on cooldown, another ability that is not will be pressed also and thus will fire off.



An alternative is to make a longer castsequence.

The Global Cooldown is 1.5 seconds.
Most melee abilities are instant.

If your castsequence of abilities is ten long, and Thrash occurs once in it...
Provided nothing else has a cooldown that will cause the sequence to 'stick', that could work too.